Why is every address in a micro-controller only 8 bits in size?

Question: I have seen that, in 32-bit microcontroller, each address of memory holds only 8 bits of data; it is the same for a 16 bit MC as well. For 32-bit data, it uses a combination of 4 addresses. Why can't an address made to hold 32-bit data directly (making it 32 bits or 16 each instead of 8)?
Comment: It's like candy bars.  They keep making them smaller for the same price.
Comment: Simply not true, which is the reason why programming languages like C and C++ incorporate the possibility for a byte to be greater than 8 bit. Its just  that the majority works best with 8 bit bytes, but 9bit or 18bit is out there.
Comment: Can this question be rephrased "Why are all addresses aligned to 8 bits" ?
Comment: @FlorianCastellane This. The addresses are not 8 bits in size (unless you can find a device with < 256 bits of memory, then they might be).
Comment: It depends on Data bus of Microcontroller. Which 32-bit microcontroller has byte memory? Do you have any example?
Comment: @ArunCheriyan What makes you think 0x00 "itself" isn't 32-bits wide? In fact, it has no specific width. On many platforms, you can read an 8-bit value, a 16-bit value, a 32-bit value, or a 64-bit value from address 0x00.
Comment: Do you have link to the datasheet? Google returned no search results
Comment: Nuc220V3EAN Cortex M0. suppose the memory address 0x00 can hold 1 byte data. in 32 bit MC address 0x00-0x03 is used to store a 32 bit data. why can't 0x00 itself be 32 bit wide ?
Comment: @Swanand The Motorola MC68008 version of the 1980's vintage 68000 microprocessor had 32 bit internal registers but an 8 bit external bus.  The National Semiconductors NS32008 was a similar beast.  These were intended for low cost systems where doubling or quadrupling the number of pins required for the bus, the number of expensive memory devices and board space were deemed to be important.
Comment: @jayjay Do you mean <256 words of memory?
Answer: There are a few DSPs (e.g., TI C54x) that cannot address values smaller than 16 bits, and some audio DSPs use 24 bits. However, 8-bit values are used in pretty much all general-purpose code, so all general-purpose CPUs support it.
And just because the smalled unit used for memory addresses is 8-bit bytes does not mean that this would be the largest unit that is actually used on the bus; most CPUs use their native word size (16/32 bits) or even a larger size to address memory, and when using byte accesses, automatically extract the byte from the larger word.
For example, the PCI bus always uses 32-bit transactions, but has byte enable signals for access that must be smaller.
Comment: @ArunCheriyan An example of a CPU that worked with nibbles as the smallest adressable word is the [Saturn](https://en.wikipedia.org/wiki/HP_Saturn): a CPU designed by HP and used in their high-end calculators back in the last century (the well-known HP48 in particular). It had a very unusual architecture (64 bit registers, 4 bit ALU, 20 bit adresses, ...).
Comment: Maybe the Intel 4004?
Comment: @davidcary Oh, well... Dates and time have never been my strong suit, anyway. Ask my wife about her birthday presents, and my boss about the deadlines...
Comment: Thank you. is there any MC that is a nibble wide instead of byte in memory ?
Comment: Another example: The smallest addressable unit for TI's TMS320C3x is 32-bits.
Comment: @ArunCheriyan: You may be interested to read up on Thinking Machine's Connection Machine series of supercomputers. They used 1 bit microprocessors (not microcontrollers because like the CPU in your laptop they did not have dedicated I/O pins). So CMs were only able to process one bit at a time. But not to worry, you computer could have as many as 64k cores.
Comment: @dim: My understanding is that the [4-bit](https://en.wikipedia.org/wiki/4-bit) HP Saturn chips were manufactured and used in HP calculators through mid-2003, which is (just barely) this century.
Answer: A 16-bit or 32-bit microcontroller often needs to manipulate data that is only 8-bits wide (a byte). For example, text strings are usually stored with a single character per byte. By having a memory addressing scheme which allows each individual byte to be addressed the microcontroller can efficiently process 8-bit wide data. What this means is that 32-bit data usually resides on addresses that are multiples of 4 bytes, eg 04, 08, 0C, etc. But if the memory is 32-bit wide then the microcontroller can read 32-bits in one read cycle. Micro's often have machine instructions that can operate on different length data, so you will find that a move data instruction (MOV) can have 3 forms, MOV.B, MOV.W and MOV.L to move 8, 16 and 32 bits of data in one instruction.
Answer: This is effectively a design choice, there is no hard reason why it has to be so. Back in the old days, when high volume commodity processors operated on 8-bit values, the mapping was more consistently 1:1. For consistency as designs evolved to modern 32 and 64 bit processors, it made sense to keep the older mapping of byte-addressing even though the data buses increased (with a changing immplementation cost trade-off). Some 32 bit MCUs may still implement only 16 bit data busses to some memory, high-end processors will have 256 bit or above, and are able to load multiple core registers in a single memory transaction. Wide interfaces are good for burst or streaming operations.
The small addressable memory size is useful not only in the case of handling byte values in code, but to work with structures in memory like ethernet packets where specific bytes need to be read or modified. Frequently this sort of operation needs to be able to perform small operations but very efficiently.
There are also scenarios where it is necessary to operate with big-endian, little-endian or mixed endian data. Now there is often dedicated hardware support for this, but again, byte addressing of memory will make this type of operation more efficient in some scenarios.
It is fairly recent that the number of address bits in a register have been a limiting factor for the address space, so wasting 2 bits to address bytes rather than 32 bit words would not have been much of a concern 10-15 years ago (and now with 64 bit pointers, its common to implement 48 or 56 bit wide, byte addresses). Introductory Computer science teaching is still a little stuck in the just-post mainframe age, and doesn't always address the evolution aspects very clearly. Lots of terminology came into use (and definition) around the time that low-volume high cost architectures (in the most general sense) started to be complemented by more resource constrained and more commodity focused processor designs.
I've not answered specifically for MCUs, the architectural boundaries are not as clear as you might assume. Even a modern ground-up MCU design has a good chance of being integrated along with a many-core server processor, or exist as only one point in a scalable set of products; either way a consistent approach to accessing memory is beneficial to the end user who needs to write or port code.
I asked a question on the retrocomputing SE about register sizes to follow up on the historical aspects of this question.
Comment: I think processors with longer word sizes predated 8-bit processors.  An 8-bit processor would be pretty useless without an efficient means of adding two multi-byte numbers, and early processors could not efficiently handle numbers larger than a single machine word.
Comment: I worked with 8-bit processors enough to know that they could easily add multi-byte numbers, but not with a single CPU instruction.  First, add the two lowest bytes, and get the lowest result byte, and a separate carry bit.  For as many other bytes are present, add the next input bytes and the carry bit from the previous step, giving the next output byte and the next carry bit.  When there are no input bytes left, convert the last carry bit into one more output byte.
Comment: @user6030: Isn't it common to have an ADC instruction?  AVR does (an 8-bit RISC microcontroller [so gcc has to use ADC for `int` and `long`](https://godbolt.org/g/uVPZuR)), so does x86, so does ARM.  I assume most 8-bit CPUs would, since there'd be even more demand for it than on a system with wider regs.  Oh, is supercat saying that early processors lacked an efficient ADC?
Comment: I think its a valid point regarding the evolution of register size (although I lack data)
Answer: The basic answer is "because that's how long a byte is".  With a large established body of code which makes that assumption, breaking it would cause all sorts of problems.
Back in the early days, there was no established body of code.  Processors frequently would use all manner of strange architectures, as shown by other answers.  By the time 16-bit processors came out though, there was enough code assuming availability of 8-bit data that failing to make that easy would have been a real barrier to adoption.
Having one 32-bit word per address doesn't give any disadvantage in memory speed.  On a 32-bit system, the lower 2 address bits often don't go to the memory.  The processor will usually read the whole 32-bit word and select (or mask off) the 8-bit byte it needs within that word.  So long as your address space can store enough data (limited to 2^32 bytes with a 32-bit system) then no worries.  In fact, on many 16-bit/32-bit processors it takes longer to do processing with byte values than with native-word-length values - reading a 32-bit word and discarding part of that word will clearly take an extra operation, compared to just reading the 32-bit word.
Conversely, if you have a system where you need to use memory efficiently, then you need to be able to access individual bytes.  If you can't, you're going to run out of memory.  With that in mind, being able to reference individual bytes is clearly necessary, so it makes sense to have your memory chunked in bytes.
Comment: Indeed.  And then there's the additional question if a processor can handle the two distinct accesses needed to load or store an *unaligned* 32 bit value automatically in hardware, or if that must be explicitly handled in software.
Answer: This is what's called having byte addressable memory.  It's normally a good thing, unless you're running out of address space (e.g. 4GB with 32-bit pointers, instead of 16GB with 32-bit pointers where every address is a separate 32-bit word).
Comment: Note that address space can go past such limits if you split the addresses into parts that will fit into one register each.  I once had some 8-bit computers that reached 64 KB of memory by splitting the addresses into two parts kept in separate registers, and saw ads for computers also with 8-bit processors that could reach 1 MB of memory by splitting the addresses into three parts.
Comment: [AVR (8-bit RISC microcontroller)](https://en.wikipedia.org/wiki/Atmel_AVR_instruction_set#Processor_registers) does that: three pairs of the 32 general-purpose 8-bit registers can be dereferenced as a 16-bit pointer.  There's also some facility to combine that with another 8-bit segment to get 24-bit addresses.
Answer: The Analog Devices Shark 32 bit DSPs have 32 bits as the smallest unit of addressable memory, so sizeof (int) == sizeof (short) == sizeof (char) == 1 (Yes, they have 32 bit chars, perfectly valid per the C standard).
Also things like int_8, int_16 and such are not defined in , a nasty surprise when porting code from other platforms.
Answer: Probably already said various ways in the other answers.  In general today, but not necessarily historically, a byte is 8 bits.  Most of the time we deal with "byte addressable memory" meaning the SMALLEST thing we can access with a single address is a byte.  But that does not mean that is the ONLY thing we can address.  Depending on the platform a single address can be used to access a byte, a halfword/word (16 bits), a word/doubleword (32 bits) and so on 64 bits whatever.  The instruction basically determines what the size of the desired access is (8,16,32,64, etc) usually in those units 8, 16, 32, 64.  But that is not hard and fast, "it depends".
Also depending on the design of the processor and/or system there is no reason to assume that the size of the access is the size of the memory or the size of the smallest access.  With larger and larger requirements it makes less and less sense over time to actually implement the memory system using the smallest size, the computer you are reading this on likely uses a 32 bit wide data bus or 64 bit wide data bus for all accesses, you want to read one byte, it does a 64 bit read and tosses the rest of the bits, why it doesnt cost anything extra keep the bus that wide all the way to near the processor core and the processor selects the right byte lane.  costs more logic and or clocks to make the bus narrower or move the bytes around in the byte lanes, (is done sometimes).  so internal rams in a microcontroller might be 32 bits wide for example if that makes sense for the system.  might be 16.  Yes for writes you do burn more cycles, you have to read-modify-write somewhere along the line.  Want to write a single byte on your pc, somewhere a 64 bit read happens, and then somewhere one byte of that 64 bits is modified, depending on what you do after that that 64 bits may go back out to dram with only those 8 bits different from what was there before, caching and your code make this not a generic rule though.  Writes are fire and forget though, the memory controller can collect the address and data from the processor and allow the processor to keep running while it eventually does the write saving clocks, maybe more clocks that are burned in a read-modify-write (if in cache already), not likely saving clocks if in a cache miss.
There are exceptions even today to pretty much all of this, there are perhaps instructions or access types in some systems that are bit addressable, there are some systems where the address is in units of something other than a byte.  A byte was not always 8 bits and maybe there are systems still running that that is true (we used to use octal and a 9 bit byte 18 or 36 bit word make a lot of sense to human programmers and chip designers that think octal, an 8 bit makes a lot of sense to hexadecimal thinkers).
Now the computer you are reading this on, even though the data bus for that dram controller might be 32 or 64 bits wide, the actual dram module itself is likely made up of multiple 8 bit wide parts, which you can easily see.  If it has 8 or 9 chips on one side it is probably a 64 bit or 72 bit (64 bits plus 8 bits of ECC) wide bus implemented with 8 bit wide parts.  If you have 4 or 5 chips one one side of the module but have still tons of pins, then it is either a 32 bit wide (unlikely these days) or 4 of the chips are 16 bit wide and if there is a 5th it may be 16 bits wide and only 8 are used or it is an 8 bit wide part.  There are 32 bit wide parts too, but 8 bit wide is most common.  A very common practice that goes way back.  Due to manufacturing costs and other factors it makes more sense that the first parts to be produced at a new density are 8 bits wide, then over time as legacy computers remain working, 16 and maybe wider parts for that speed/interface become available as density increases.
We would need to know what microcontroller.  Since you mention 32 bit it is quite likely (without detailed info though we cannot tell) that the memory inside that part is 32 bits wide, and all accesses to it are 32 bits wide.  the instructions would likely determine what the program wants which probably offers an 8 bit, 16 bit and 32 bit access type, the smaller ones on writes would require a read-modify-write somewhere, reads you just ignore byte lanes.  Same goes for the flash, although flash writes are another topic.  But the internal flash is most likely 32 bits wide and all reads are in units of 32 bits.  An external flash though, that is another story, most likely they are one bit wide (spi or i2c), although spi parts can sometimes support 1, 2 or 4 bits, but one miso pin is most common. Internally they are organized in units of bytes, could be 8 bit wide or 16 or 32, or who knows, you shift out and address them in units of bytes though.  with spi you can shift out anywhere between one byte and the whole memory in a single transaction, depends on the flash part design.
Answer: The size of the addressable memory unit is essentially a compromise between how much memory you can address vs. how much memory you will waste.
Addressable memory. Consider a 32-bit CPU: if you address bytes, you can address up to 4GB of memory. If you address individual bits, that amount will be reduced to 512MB, and if you address 32-bit words you'll have 16GB. (your question seem to suggest the latter).
Wasted memory. If you have a variable which can be represented with X bits, and you only can allocate units of N bits for it, you'll waste (N-1)/2 bits on average, assuming X > N. If you address individual bits, you will use the memory with 100% efficiency (at least from addressing point of view). With bytes, you will waste 3.5 bits per variable (56% efficiency), and with 32-bit words, you'll waste 15.5 bits (52% efficiency). But it gets worse: if most of your variables are small (think characters, booleans, status flags), you'll end up wasting most of the memory if your addressable units are too big.
For example, let's assume the average size of a variable is 8 bit.

on a bit-addressable computer, you will be able to allocate with 100% efficiency, which will give you 512*1024*1024*100% = 0.54 billion variables.
on a byte-addressable computer, you will allocate with 56% efficiency, which will give you 4096*1024*1024*56% = 2.4 billion variables. That's almost 5 times as much compared to a bit-addressable computer! Of course, you'll need to buy 8 times more memory.
on a 32-bit-addressable computer, since at least half of your variables will occupy less than 8 bits, they will be allocated with efficiency below 7% (using 4.5 bits out of 32). In any case, you won't get more that 4.3 billion variables (since you only have have that many distinct addresses), and less than that in reality. Avoiding complex calculations, I'd guess will get perhaps 20-30% more useful storage compared to byte-addressable computer, while paying 4 times the price for the RAM.
Answer: You can get 1 bit processors too!
The data width will follow the register (accumulator) width. this is normally the 'processor width' whereas the address buss may be different (usually wider), but could technically be narrower depending on the use.
8 of course is a power of two number.
We have history to thank for the ubiquitous use of 8 bits - and COST/ability of technology.
For a long time 8 bits ruled, part of the reason being the width of busses and the difficulty in making registers (and RAM) more than 8 bits wide (no point in 16 bit data if your registers are all 8 bit).
8 bits is rather nifty, and makes a lot of sense in Hex.
8 bits could hold your alphabet, numbers, drawing & control characters (ASCII), or 0 to 255 or +-127
Accessing more than 256 bytes of data (8bit address bus) is easy with paging, Select the page, then the byte e.g. 256 pages of 256 gets you to 64K (65536). Usually page zero would be a scratch pad as it would be faster to access as this would not require the page to be set.
My first computer had 1k x 8bits of static ram! (dynamic RAM was cheaper, but needed more hardware to refresh it).
With a few flags (c, nc, z, nz), add, subtract, rotate left and right, you can do some pretty complex math on an 8bit machine. You don't need a floating point arithmetic unit! Not super fast, but doable!
Many early processors could be single stepped, and used with simple static RAM made debugging really easy; adding some octal buffers and early red LEDs, you could watch the address and data busses changing :)


How to view saved passwords on Chrome iOS?

Question: On my desktop I have an extension which prevents websites from reqesting the browser not to recognize the password fields (I imagine they view this feature as unsecure). Now I have synced my passwords with Chrome in iOS, and the extension is not available on iPad. This means that while the
password has synced, it does not automatically get entered into the password field. So I thought I would just view the saved password and enter it manually. Unfortunately I am unable to do so. If anyone knows how to either view my passwords or otherwise recover it, I would be most grateful.
Answer: You can't review your stored Passwords in the Chrome App at all.
On the App and in the Support Documents Apple mentions  to use the url passwords.google.com see
On that Page when you open it on your Moblie it says that you can access your Passwords From all your Divices but not fron this Site see
So i think there is currently no way you can have a Look at your saved Passwords at the Moment.
If you realy need it you should Fill a Bug request and send it to Google so they maybe will fix it in the App.
Comment: This is exactly the pictures I was going to post in a question because what they've written sounds extremely stupid. Well, we're still here, two years later. Google is still doing its thing.
Answer: As of June 2019 on iOS 12 on an iPad Air 2 (app version 74.0.3729.155) I found the following method to work. I do not own an iPhone, so I can't comment on whether the same works there.

Click the menu icon (three dots), then  "Settings".
Enter the passwords submenu.
After a short delay, a list of your accounts should be displayed. A search-bar should be located at the top of the dialog.
For each entry you can view and copy the password, which will prompt for further authentication (TouchID in my case).

Honestly though, I find that protection too weak. Convenient or not, an account list should never be displayed without explicit authentication. Google seems to still believe that being logged into a device is sufficient authentication, and that nobody ever allows anyone else to access their devices. At least requiring the finger print for accessing the password is an improvement though.
If passwords.google.com works for you, you should urgently make sure that passphrase based end-to-end encryption is enabled on your devices with Chrome. Otherwise you may be syncing sensitive data in a form that is accessible on the server side; While using Chrome in itself already puts significant trust into Google as a company, server-accessible synchronization opens up your data to rogue employees or future server breaches.
As far as I know, Chrome now by default encrypts passwords with your Google password though, so the website should actually be non-functional for everyone, unless they have implemented client-side decryption in the interface and explicitly prompt for the password. But that would be equally possible with the passphrase, so it probably does not apply.
Answer:
Launch your Google Chrome browser.
Open the menu with the 'three-dot' button on the far right of the Chrome toolbar.
Click "Settings".
Scroll down to the bottom and select the "Advanced" option at the bottom of the drop-down menu.
Navigate to the "Passwords and forms" feature and click "Manage passwords".
Find the website that you wish to show the password by clicking the "eye" icon or you may click the three-dot button to get details about the saved password or remove it.

Also, from the "Manage passwords" feature, you can select any account/website that you wish to edit, remove, or update a password for accessing the specific site again.
Answer: You can now actually view (!) passwords on passwords.google.com on iOS, by tapping the eye icon next to them.
A word of warning though, in the typical Google fashion they've made a half-assed implementation, complete with the trademark defective and poorly thought through UI. Don't expect to be able to select your entire password if it's longer than, say, 12 characters and happens to contain some sort of punctuation. Copying the password will of course also be out of the question in those cases.
Oh and rotating the device can't be used as a workaround. Also there's no search. Or feedback button.
Thanks Google.
Answer: In Chrome for iOS:

Go to Settings
Tap Save Passwords
There should be a list of all passwords you saved. You can delete then using the edit button or swiping left on the password you want to delete
Comment: This does not explain how to view saved passwords.
Comment: @MarekBettman There is no Show button on Chrome for iPhone. Chrome for Windows has one, but on the iPhone, there is no button.
Comment: @MistaJ - just click on password field and you should see 'show' button
Answer: View and manage passwords at passwords.google.com
From there sign in to your google account and you will be able to look at all the passwords you have saved. Hope this helps.
Answer: You can see them also on passwords.google.com.


Office pro 2007 Product key does not work after recovering from backup

Question: I had a hard drive failure but backed up the data before it was fixed. When I put the data back on, Office would not work. Is there anyway to find the code from the back up data ?
Answer: How did you back up the data? Unless it was a drive image which you can restore, it's extremely unlikely. I believe this information is stored somewhere in the registry.
We use Magical Jelly Bean Key Finder at the shop to grab the key before a wipe, but it's not possible from the backup data itself (unless you have mad skills on mounting the registry files).
Now the obvious question: why not reuse the code you have from when you first installed it?


Are faster processors hotter?

Question: Let's take the Intel Core 2 Duo P7350 and P8600 for an example. Both have a 3MB cache and a 1066MHz FSB, but the P7350 runs at 2.0GHz, while the 8600 runs at 2.4GHz. Is there a tradeoff between heat generation and performance?
Comment: Each year, Intel has either a "tick" (smaller silicon pathways) or a "tock" (new architecture).  Each one reduces power consumption per performance.  But within a generation, clock speed (or number of cores) does dictate power consumption and temperatures.  When both clock speed and the architecture/process are different, you'll have to do some tests.
Comment: They look all the same to me.
Comment: @muntoo: *groan*
Comment: @Nikhil: You missed out. If you'd posted that as an answer, you would have gotten quite a bit of rep! :)
Answer: Yes!  All else being equal (that's key!), a processor with a higher clock speed will use more energy and therefore also produce more waste heat.
Sometimes manufacturers can redesign a processor in a more-efficient way, or move to a different manufacturing process, or other factors can influence how much waste heat is generated such that faster processor could even use less energy.  But, given the critical "all else equal" condition, a faster processor runs hotter and there is a tradeoff between speed and heat/energy use.
In fact, there's a growing market out there for processors that are intentionally underpowered to serve as cpus in computers that don't need great performance.
Comment: @Wil, Methinks you misunderstand the concept of 'All else being equal'
Comment: Also, Apple CPUs run hotter than Orange CPUs.
Comment: Not 100% always, my Pentium D runs MUCH hotter than a Core 2 Duo.... But the later P4's and PD's are from a generation of rubbish, energy inefficient room heaters!
Comment: ... but everything else you said is very good!
Answer: The very short answer is YES!
Faster processors will indeed get hotter than a similar processor that is not running as fast.
Something to consider is the advances in materials science over the last 15 years.  Much effort has gone into packing more transistors per cm on the chip, reducing power requirements and increases in efficiency which also reduce waste heat.  So that being said, know that all processors are not equal at all.
Answer: If you are comparing the processors using the same manufacturing technology and architecture, then yes.
But once you start comparing really old stuff to today of course it does not compare.
For example, a last few P4s are the hottest processor ever made, but they are much slower than your standard C2D which runs much cooler.  In a few generations the same might occur.  While improvement in manufacturing technology will generally reduce heat output, it also allows companies to fit more dies in the same area.  What this means is the heat output might actually stay the same, but we'll definite have faster and faster processors.

Are faster processors hotter?


From what materials can a mikveh be made?

Question: Reading sources on constructing a mikveh, it seems that the walls and floor should be made of brick or ceramic.  Is any other material possible, such as aluminum, wood, Lexan (plexiglass), or fiberglass?  Reason I ask is that I want to retrofit my existing fiberglass bathtub/shower as part of the structure, since it can't be ripped out of the bathroom wall.
Comment: I am not sure I understand how the mikve construction laws apply to your bathtub/shower. A mikve needs a souce of rainwater, can you get that into your bathtub?
Comment: @mbloch (no) rain!
Comment: I'd build a rainwater tank inside the bathroom next to the tub.  I'd extend the house rain gutter into the tank through the bathroom window from the outside.  I'd build up the tub to become high enough for immersion when sitting.
Comment: Amazing. Kol hakavod. But the laws of mikve construction are very complex and you will need an expert to advise you. I can't imagine it could be done via MY. Maybe you can ask for names of experts here ;-)
Answer: Rabbi David Miller wrote a book called the Secret of a Jew(Sod Netzach Yisrael) ,the purpose of the book was to get Jews who weren't religious to start keeping the Torah. Its a great read even for those who are religious since it gives a glimpse into the world of American Jewry in the early 1900's. Anyhow, Rabbi Miller understood that many women werent going to the mikva for various reasons. So Rabbi Miller sought to find a way that every woman would be able to build their own mikva and immerse in the privacy of their own home. His method of using the water system was very controversial,but nonetheless his intentions were pure .
In the book he gives instructions how to make a very inexpensive mikva from basic materials. In this link one will be able to see his instructions and his thought process. It goes without saying that when it comes to the issur of kares(relations when wife is a nidda) extra caution needs to be taken and an expert Rabbi in the field of mikvos must  be reached before such a project is started. This is just to get an idea of the basics.
Here is a picture of what his basic mikvah construction looked like with details of items needed with their prices from 1930 (see link above):

For the frame
Item a.    8 pieces    1" stock, 12" wide, 30" long (1" x 12" x 2'6")
Item b.    4 pieces    1"         2"       48"      (1" x 2" x 4')
Item c.    8 pieces    1"        12"       48"      (1" x 12" x 4')
Item d.    2 pieces    1"         6"       48"      (1" x 6" x 4')
Total 59 feet at a cost of about 3 cents per foot -cost- $1.77
Item e.  A box of 6-penny nails - cost- .10
For the lining
Item f.  72 ft of roofing paper costing about $2 for a roll of 100 ft- cost- $1.44
For the outlet
Item g.  1 1/2 inch hydrant bib faucet ..................................   .50
Item h.  1 1/2 inch by 3 inch all-threaded galvanized (tank) nipple .....   .10
Item i.  2 1/2 inch lock nuts and 2 fiber washers .......................   .10
Item j.  1 1/2 inch sleeve or coupling ..................................   .15
Total .......................................................... $4.16
Add 10% for unforseen expenses or variation in prices ..........   .42
Total .......................................................... $4.58
Comment: His heterim were quite controversial.
Comment: @ShmuelBrin ,yes I did note that in my answer ,still doesn't take away from his intentions and his brilliance. He was also talking to an audience who vadai weren't  going to the mikva.
Answer: It can be made from any material that does not leak, the main issue is that it should not be a vessel
It would seem legally ok to use the tube if you make a hole (by the drain) the size of a pomegranate and then seal it with cement and the cement should also be connected to the structure that is connected to the ground
But the the rain water that is collected in the tank is probably not considered rain water anymore but collected water and it can not be used

There is a law that you need (try) to dip into water that is the hight of a hand above the naval when standing
Comment: According to my research, redirecting rainwater through gutters that don't collect water themselves is not considered collection.  C.F. Chabad publications re mikvek constructions.
Comment: @eternalsquire That is correct buy your tank might be a vessel,
Comment: What's the difference between a pool, or 'bor', and a vessel?  In the "kissing" construction there are effectively two pools which connect through a common wall.  I don't see any effective difference between a raised tank and a raised pool in this case.
Comment: @eternalsquire that is the law, maybe because water in a vessel is more in human hands then water in a pit,
Comment: no way to dig a pit indoors.  I'll ask this as a new question.
Comment: @eternalsquire The basic laws of mikva is (by rain water (not spring)) that the water needs to be not in a vesal, and the first  volume (40 soa) needs to be rain water that was not collected  by a human and did not pass over something that can become ritually impure (snow, ice, sea salt ... Is an exception)
Comment: Let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/39369/discussion-between-eternalsquire-and-hazoriz).


Why are the Dead Sea Scrolls (DSS) significant?

Question: Is there anything that the Dead Sea Scrolls made clearer regarding the texts of the Old Testament?  Did their discovery change the way we view the development of the Tanakh?
Comment: Hi. You've just asked two closely-related questions. I was wondering if there was anything more specific that you were hoping to find. Answers to both questions are quite easy to find with a quick Google Books/Google Scholar search.
Comment: Tangentially related: [Why is the LXX significant?](http://hermeneutics.stackexchange.com/a/279/68)
Comment: @brilliant i say that they're closely-related because they're seeking the same sort of information but within different milieus. i'm not saying that they're exact duplicates, but they're within the same vein so i imagine that there's some sort of underlying quest here. just trying to help you write a good question that'll get some better traction.
Comment: @swasheck - Why are they closely-related? One is about particular scrolls (Dead Sea Scrolls), another one is about anything, which is not biblical scrolls, one is about the Old Testament, the other one is about the New Testament.
Comment: @swasheck - I see. Well, I just wanted to know how recent advancements in history, archeology, textual criticism, etc. have helped us clarify some points in the Bible that might've not been that clear to us, say, 200 years ago.
Comment: [Do the Dead Sea scrolls describe any prophecy which was fulfilled after they were written?](http://christianity.stackexchange.com/a/3592/30)
Comment: [The Dead Sea Scrolls and Protestant canon](http://christianity.stackexchange.com/q/3063)
Comment: Relevant: [Has Pesharim left any mark on modern hermeneutics?](http://hermeneutics.stackexchange.com/q/55/68)
Answer: They also show us that the canon was settled long before Jamnia.  In the scrolls, we have at least partial copies of every book in the Old Testament except Esther.  We also have many scrolls that are not canonical, however, even that teaches us something.  Their literature can be broken down into three types.  (The percentages are from my seminary notes with Dr. Waverly Nunnally who studied at Hebrew University in Jerusalem and Hebrew Union in Cinncinatti.  His dissertation was on the use of Abba in the Dead Sea Scrolls, and he and his best friend wrote a computer program to reconstruct the scrolls from a concordance before their public release.)

Old Testament manuscripts. Dt., Is, and Ps are the most frequent and quoted most often in the sectarian texts.  The New Testament and rabbinic literature quote those three the most and in about the same frequency as Qumran.  We have pieces of every book in the Old Testament except Esther (but we don't have everything from Qumran). This makes up 12% of the texts.
Apocrypha and Old Testament psuedopigrapha.  This category is very important in what it teaches us.  It was assumed by some scholars that these apocryphal and pseudopigriphal works had origianlly been written in Hebrew, but until this, no evidence outside of the text (the Greek copies contain many Hebraisms, phrases that look like they were originally Hebrew or written by someone whose first language was Hebrew).  Text critics and translation theorists loved this find.  Examples from this category were ~66% of Ecclesiasticus and two versions of Tobit (and the longer version is the older of the two).  These works make up 3% of Qumran.
Secterian Material.  These works are unique to Qumran and the Essenes.  Examples of this would be Community Rule, War Between the Sons of Light and the Sons of Darkness, and the letter they wrote to the Pharisees (MMT).  Two things it shows us is that they considered themselves to be the true remnant and believed that the temple was broken.  85% of the material falls into this category.

The Essenes wrote a style of commentary called Pesher.  All such Pesher falls into category 3.  There are three ways that they show us the Old Testament was settled before Jamnia.

They only write Pesher on canonical works.  I do not have the breakdown on which books they wrote Pesher on, but they only wrote it on canonical works.
Even though many other apocryphal and pseudopigraphal works were available, they collected 4 times as many canonical works.
In the letter to the Pharisees (MMT), they specifically state, "these are the books we hold to be sacred..."  They then state the three divisions of the Old Testament, "book of Moses," "the word of the Prophets," and "David and the Events of the Days of All the Generations."  David, of course, refers to Psalms, the first and largest book in the writings.  Events of the Days is another name for Chronicles, the last in the set.  The natural conclusion from this is that if they name the same divisions as are used even today, and as we can be sure that the books of Moses counts five and not six or seven, and the writings begins and ends with the same books as later, then the canon was already settled.
Comment: I've done some hunting around and I have a few questions: 1) where did you get the 12/3/85% division? 2) Does Pesher exist for _all_ the Tanakh (except Esther)? 3) I see some interpretations that show the MMT divided the canon into 3 parts, but I don't see any that give the number of books in each part.  Do you have a source? 4) Doesn't the evidence support an _open_ canon as much or more than a closed canon?  I'm glad you answered (+1), but I'm not entirely convinced. ;)
Comment: The numbers came from my notes from Dr. Nunnally's class on NT backgrounds.  I was going from memory on the MMT, so it might not state the number in each (I was likely conflating it with Josephus's statement).  Others I will modify the above.
Comment: As for an open canon in Jesus' day, I concluded "no" long ago.  I have the detailed information on that at home and should be able to look it up tonight.
Answer: I think I may be posting an answer not quite in-line with what you were hoping for but I am not sure if anyone has published the various differences between the manuscripts that could answer your question properly. I apologize about that.
However, I think it might be worth mentioning that the main benefit of the Dead Sea Scrolls is not small clarifications here and there but that they provide a very large portion of the Old Testament scriptures that are older than those previously extant without 'hardly any difference'.
The scrolls are many:

Over six hundred scrolls and thousands of fragments have been discovered in the 11 caves of the Qumran area. Fragments of every Biblical book except Esther have been found, as well as many other non-Biblical texts.  (Source)

The scrolls show how well the scriptures have been preserved to us today without any difference:

One of the most important contributions of the Dead Sea Scrolls is the numerous Biblical manuscripts which have been discovered. Until those discoveries at Qumran, the oldest manuscripts of the Hebrew Scriptures were copies from the 9th and 10th centuries AD by a group of Jewish scribes called the Massoretes. Now we have manuscripts around a thousand years older than those. The amazing truth is that these manuscripts are almost identical! Here is a strong example of the tender care which the Jewish scribes down through the centuries took in an effort to accurately copy the sacred Scriptures. We can have confidence that our Old Testament Scriptures faithfully represent the words given to Moses, David and the prophets. (Source)


Will it be a problem if I never used an Indian tourist visa that I was issued?

Question: In 2016, I applied from Bangladesh for an Indian tourist visa; it was issued and it expired in 2017. However, I did not visit India during that time. Now I need a new visa for a 2018 visit. What do I need to do?
Comment: Just apply for a visa.
Answer: Plans change all the time. Not using a Visa is not at all an issue.
A personal experience. I applied for Malaysian visa, got that. But I couldn't use that visa, as my plans got changed. When I applied second time, they didn't even asked any questions. Your visa is here.
Don't give explanation on why didn't you use previous visa, unless it is asked (most probably they won't care).
Answer: There are any number of reasons does not get used. Medical problems, family matters, work issues all... these are no problem. The overall reason visas are issued are to give the receiving country a chance to research your circumstances whether you are likely to return home after your visit. Not using a visa doesn't change this at all.


Is the healing technique of Karate Kid practically possible?

Question: In The Karate Kid (2010),  Jackie Chan uses some fire technique for healing Dre's wounds. I want to know if that technique is real or complete fiction.
Comment: Thanx for the edit, i didn't know how i killed the title and some part of question body.
Answer: The method is called Cupping therapy and is a form of alternative medicine:

A partial vacuum is created in cups placed on the skin either by means of heat or suction. According to the American Cancer Society, "[a]vailable scientific evidence does not support cupping as a cure for cancer or any other disease". It can leave temporary bruised painful marks on the skin and there is also a small risk of burns.

Being that it is an alternative medicine, some people will say it really works and some people will call it "fiction".
Comment: Think placebo: it works, to some degree, only if you believe it.
Comment: It's perhaps worth noting that, whether it works or not, there are several professional athletes who believe that it does, and use it, including Michael Phelps. http://www.independent.co.uk/news/world/americas/rio-2016-cupping-what-is-it-olympics-athletes-suction-cups-skin-marks-a7178731.html
Answer: By cupping with the help of fire or suction, a vacuum is created which creates localized inflammation proximal to the injured/diseased area. Inflammatory substances are drawn to the new area of inflammation by the body, the body rather 'prioritizes' the area to be managed by inflammation. This helps the sufferer to relieve of the suffering due to inflammation of the original site.
Indian techniques of Ayurveda like 'agnikarma', now commonly done for conditions like plantar fasciitis also is thought to depend upon this ability of the body to 'camouflage' the original area of inflammation by creating a new area of inflammation nearby.
Answer: I believe it's something to do with acupuncture. There's two types indirect and direct
In direct moxibustion a small amount of moxa is placed on top of an acupuncture point and burned. Direct moxibustion is a traditional technique considered to be very therapeutic. This type of moxibustion is further categorised into scarring and non-scarring. With non-scarring moxibustion, the moxa is placed on a point, ignited and allowed to remain onto the point until it burns out completely. This may lead to localised scarring, blisters and scarring after healing. The person will experience a pleasant heating sensation that penetrates deep into the skin but it isn't likely they will experience any pain. The effectiveness of direct moxibustion particularly on immune function has been reported as early as 1927 by Dr Shimetaro Hara at the Kyushu University in Japan.
Indirect moxibustion
Indirect moxibustion is the popular form of care, there is a much lower risk of pain or burning. In indirect moxibustion a practitioner lights one end of a moxa stick, holding it close to the area being treated for several minutes until the area turns red. There are other forms of indirect moxibustion. For example another form of indirect moxibustion uses both acupuncture needles and moxa. A needle is inserted into a point and retained; the tip of the needle is then wrapped in moxa and ignited, generating heat to the point and the surrounding area. After the desired effect is achieved the moxa is extinguished and the needle removed.
Comment: Can you re-format this to make it easier to read? Maybe clear up some of this confusion: With **non-scarring moxibustion,** the moxa is placed on a point, ignited and allowed to remain onto the point until it burns out completely. This may lead to **localised scarring,** blisters and scarring after healing.


Can using Varnish still help to improve the performance of my site if I already use CloudFlare?

Question: I'm using CloudFlare right now. Can Varnish still help to improve the performance of my site?
Answer: Yes, it could still help. Although CloudFlare caches static content, it doesn't cache dynamic content served by your server, which could be of benefit as covered here.
Some methods to use both in conjunction are covered here and here.
Answer: Just a quick correction:
CloudFlare won't cache dynamic content by default. You can, however, use PageRules to cache dynamic content (use with some care).


Is Ubuntu 12.04.1 windows wubi installer broken?

Question: I installed the newest release of Ubuntu 12.04 with the wubi installer. The computer is up and running with Ubuntu, I am typing this in Firefox and I can use all the software that was supplied with the installation. However, it seems there is only a small selection of new apps that I am able to install. I have not done anything else on this installation except 1) run wubi to get Ubuntu in there and 2) start it up and 3) try to install these applications that just won't install.
For example, I managed to install Inkscape and gParted. However, I could not install the latest proprietary nVidia drivers, I could not install Skype, I could not install Qt Designer, nor could I install a number of other things I tried to get.
For some of the failed installations I get an error which there is already a bug report for: "package xxx could not be installed because package xxx is already installed" or something similar. For others, it is a different error, for example "The following packages have unmet dependencies: skype: Depends: skype-bin but it is a virtual package".
This issue forces me to return to Windows, for now. But I would like to know if this is an issue specific to the wubi installer, so that I should try again but with a different installation option, such as getting a USB pen driver ISO or something such? Or is there something else going on right now for pretty much everyone? Or maybe someone could even give me a hint as to how to solve the issue without downloading yet another ISO?
PS. My ubuntu installation is on a different physical SSD than my windows installation. The system is a Dell XPS 17.
Comment: The answer is that Wubi has nothing to do with your particular problem.
Answer: Did you install updates after installing ubuntu. I had problems with some packages on a fresh install. Updates fixed it all.
Comment: I tried to run update, but it said there are no packages that needs updating.
Comment: "sudo apt-get update" and then check again


What is the Catholic Church's official position on the Spanish Inquisition?

Question: The Spanish Inquisition seems to have had plenty of support from the Universal Inquisition at the time, but what is the present Vatican's view? Has the Church repudiated the Inquisition?
Comment: What makes you think the Inquisition was a separate entity from the Catholic Church, as you seem to imply?
Comment: @Geremia, I think it's just a function of me not being familiar with the terminology. Would you recommend a different phrasing?
Comment: [Here](https://www.nationalreview.com/2018/06/spanish-inquisition-courts-were-moderate-for-their-time/) is an article called "The Spanish Inquisition Was a Moderate Court by the Standard of Its Time" that asserts not only that the Inquisition treated defendants relatively well, but that the worst of the Inquisition was the fault of the Spanish crown and that the church's reason for getting involved was a (perhaps naive) desire to combat a frenzy of pogroms and religious denunciations in Spain at the time.
Answer: Yes. The Catholic Church has repudiated the Spanish Inquisition. In fact the late Pope John Paul II has apologized for the atrocities committed during the Spanish inquisition.
In the Apostolic letter "TERTIO MILLENNIO ADVENIENTE" he made this apology:

Hence it is appropriate that as the second millennium of Christianity draws to a close the Church should become ever more fully conscious of the sinfulness of her children, recalling all those times in history when they departed from the spirit of Christ and His Gospel and, instead of offering to the world the witness of a life inspired by the values of her faith, indulged in ways of thinking and acting which were truly forms of counter-witness and scandal. Although she is holy because of her incorporation into Christ, the Church does not tire of doing penance. Before God and man, she always acknowledges as her own her sinful sons and daughters.

He also reiterated his apology in his letter to Cardinal Roger Etchegaray on the occasion of the release of the "Report of the International Symposium on the Inquisition".
Comment: I don't see any explicit reference to the Spanish Inquisition in the quotation here.
Comment: Also, from [that document you quote](http://www.vatican.va/holy_father/john_paul_ii/speeches/1998/october/documents/hf_jp-ii_spe_19981031_simposio_en.html), he says: "The Church's Magisterium certainly cannot perform an ethical act, such as asking for forgiveness, without first being accurately informed about the situation at the time [of the Inquisition]." How can the Magisterium be a person, let alone a sinner?
Comment: Is he admitting the Magisterium can err? If so, this is heresy because the Church is indefectible.
Comment: The Ordinary Magisterium can err, as the Church herself recognizes.
Answer: What is currently called the Congregation for the Doctrine of the Faith used to be called Congregation for Universal Inquisition (erected in 1542), which changed its name to Congregation of the Holy Office in 1908. The Spanish Inquisition was just the Spanish branch of the Inquisition.
Also, a good book on the Inquisition, which dispels the myth that the Catholic Church executed people (it was the State who actually did that), is canon lawyer Ed Peters's Inquisition. There's also a good Old Catholic Encyclopedia article "Inquisition."
Related to this is St. Thomas Aquinas's discussion of the question "Whether heretics ought to be tolerated?":

With regard to heretics two points must be observed: one, on their own
  side; the other, on the side of the Church. On their own side there is
  the sin, whereby they deserve not only to be separated from the Church
  by excommunication, but also to be severed from the world by death.
  For it is a much graver matter to corrupt the faith which quickens the
  soul, than to forge money, which supports temporal life. Wherefore if
  forgers of money and other evil-doers are forthwith condemned to death
  by the secular authority, much more reason is there for heretics, as
  soon as they are convicted of heresy, to be not only excommunicated
  but even put to death.
On the part of the Church, however, there is mercy which looks to
  the conversion of the wanderer, wherefore she condemns not at once,
  but "after the first and second admonition," as the Apostle directs:
  after that, if he is yet stubborn, the Church no longer hoping for his
  conversion, looks to the salvation of others, by excommunicating him
  and separating him from the Church, and furthermore delivers him to
  the secular tribunal to be exterminated thereby from the world by
  death. For Jerome commenting on Gal. 5:9, "A little leaven," says:
  "Cut off the decayed flesh, expel the mangy sheep from the fold, lest
  the whole house, the whole paste, the whole body, the whole flock,
  burn, perish, rot, die. Arius was but one spark in Alexandria, but as
  that spark was not at once put out, the whole earth was laid waste by
  its flame."
Comment: Let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/20134/discussion-between-geremia-and-fredsbend-the-grinch).


Inflection point of a function

Question: For what values of $a$ does the function $f(x)=e^x+ax^3$ have an inflection point?
It is an old question in my mind and wanted to bring it out.
Comment: Try to differentiate $f$ twice.
Comment: For which $a$'s does $f''$ change sign?
Comment: Nice question. I saw it right now.
Answer: $$
f(x) = e^x + ax^3.
$$
$$
f'(x) = e^x + 3ax^2.
$$
$$
f''(x) = e^x + 6ax.
$$
Suppose first that $a>0$.
Since $f''(x)\to\infty$ as $x\to\infty$ and $f''(x)\to-\infty$ as $x\to-\infty$, and $f''$ is everywhere continuous, there must be a point where $f''$ changes signs.  And since $f'''(x)= e^x+6a$ is everywhere positive, $f''$ must be a strictly increasing function and hence can have only one point where it is equal to $0$, and there it must change signs.
Therefore there is only one solution to $e^x+6ax=0$, and that is where the inflection point is.  I don't think there's a closed-form solution, but you could apply Newton's method to solve this equation.
If $a=0$, then $f''(x)= e^x$, and this is always positive, so there are no inflection points.
Now suppose $a<0$.  Since $e^x\to0$ as $x\to-\infty$ and $6ax\to\infty$ as $x\to-\infty$, we have $f''(x)\to\infty$ as $x\to-\infty$.  But $f''(x)\to \infty$ as $x\to\infty$ as well.  Therefore the behavior of $f''(x)$ as $x\to\pm\infty$ does not necessitate any changes in sign of $f''(x)$.  If $a$ is a long way below $0$, you get a steep line plunging downward faster than $e^x$ grows when $x$ is near $0$, and $f''$ will become negative at some point where $x>0$, and then will become positive again to the right of that point.  You'll have two inflection points.  I think Newton's method will find them.  But if $a$ is negative and closer to $0$, the line going below $0$ will not move fast enough to outweigh the $e^x$ that is growing, and the graph of $f''$ will never go below the $x$-axis.  How do we know which values of $a$ are far enough below $0$ that there will be two inflection points?  So far all I can suggest is numerical experiments.
Comment: I is so late for thanking you, but `Thank you very much`. +1
Answer: $$f''x=e^x+6ax$$
now,
$f''x=0$ when $e^x=-6ax$   ------[eqn1]
fram the graphs of $y=e^x$ and $y=-6ax$ it can be said that a solution to this will surely exist if $a>0$ ,
but when $a<0$ we things get complicated,
if a is too small the line $y=-6ax$ may not meet $e^x$ at all,
if a is too large, the line will meet the curve twice,
so we need to find the borderline case, when the line just touched the curve, i.e it is  tangent to $e^x$
Let the line touch the curve at some $x=x_1$
slope of the line $y=-6ax$ is $-6a$
slope of $y=e^x$ at for some $x=x_1$  is $e^{x_1}$
so we have $-6a=e^{x_1}$
also since the line and the curve are touching we have,
$-6ax_1=e^{x_1}$
from this and previous results we have,
$-6ax=-6a$
this gives the solution either $a=0$ or $x=1$
putting x=1 in [eqn1] we get,
$e=-6a$ or $a =\frac{-e}{6}$
hence the complete and final solution is ,
$$a \in [0,\infty)\cup(-\infty ,\frac{-e}{6}] $$
Answer: Actually there is a very nice closed-form solution to this problem.
As shown $f^{\prime\prime}(x)=e^x+6ax$. And inflection points are then solution to equation $$e^x=-6ax.$$
This have an analytical solution using so-called Lambert W function, i.e., the inflection points are:
$$x^\star = -W\left(\frac{1}{6a}\right)$$
From conditions on existence of Lambert function we know that if $\frac{1}{6a}\geq -\frac{1}{e}$, then $x\in\mathbb{R}$, otherwise $x\in\mathbb{C}$.
This leads to the same conditions on $a$ as Tomarinator mentioned, i.e., if $a\in(-\infty,-e/6]\cup(0,\infty)$, then $x\in\mathbb{R}$. For other $a$ (except $0$), $x\in\mathbb{C}$, where in both cases, $x^\star=-W\left(\frac{1}{6a}\right)$.

Inflection point of a function


Is there a way to round corners on material level?

Question: Is there a shader that can be used on material level that will give the effect of round edges when assigned to an object? I'm not looking to increase the mesh density, I remember in 3DS Max, Mental Ray, round corners is an option that can be enabled in material, so the object's sharp edges will "look" like smooth, without changing the object's mesh, is there a way to do this in Cycles?
Comment: @Georges  The top answer there has a link to a BA thread with the OSL shader.
Comment: Related: http://blender.stackexchange.com/questions/20997/shader-rounded-edge-between-the-two-intersecting-faces
Comment: Following the link, it says that it's possible, but it doesn't say how, do you know how to do it @Xtremity
Answer: A straightforward solution has been added to the most recent Blender distributions (after the released version of 2.79b, so you must download newer updates of 2.79b, or 2.80 Alpha, from https://builder.blender.org/download/ to enable it).
There's a single node (Input > Bevel) that fakes bevelled normals. Of course it won't change the geometry, so it doesn't look great from too close, but it can enhance pretty convincingly the specular/reflection at the edges.
Answer: I figured out how to do this with a specularity map (kind of).
The limitations are apparent as you look at the focal center of this image, the edges look rounded. However, the corners don't actually change their geometry as seen at the extremities of the geometry.

Which actually led me to this thought - If a spec map can influence this, then so can generated Ambient Occlusion (Pointiness), see the following:

Both cases being, that the first option would be necessary when there are external angles of pointiness, and the second option being, when there are internal angle by which AO/Pointiness will give you this spec map like result.
Comment: The problem is, these solutions are changing the material itself, they will work in very specific conditions. The first solution is the closest to the needed result, I'll experiment with it, I tried the osl solution, but I got no results, I don't know is it because I am doing the links wrong, or because osl sometimes just doesn't work well with some graphic cards.
Comment: I think maybe the 2nd option was with the world AO settings turned on, sorry about that. That option is a little deceiving. It's still valid somewhat, as you can seperate those to a different scene and use the compositor to reunite anything that uses world AO.


Is there such thing as a SuperDrive enclosure?

Question: The OWC Data Doubler allows you to remove the SuperDrive of a MacBook or MacBook Pro and install a secondary drive. This leaves you with two drives in your Mac laptop, and a SuperDrive sitting on your desk. Is there any sort of SuperDrive enclosure that would allow you to put a SuperDrive inside of it, and then plug into your computer via USB?
Answer: Yes, I have this one.  I got it at Fry's in exchange for one by sabrent that didn't work with my mid-2010 superdrive. This new one works just fine with my removed superdrive on 10.6.4, even though the box says it's compatible with basically every version of windows but does not mention OS X.
The one caveat... it comes with a wall adapter for powering the driver rather than a second usb cable. However, I have a USB to male power cable. I plan to remove the power connector and swap it for the connector that is on the plug in adapter that came with the enclosure. The adapter just outputs 5V 2000mA, so I don't see any reason why a straight USB connection wouldn't work just fine.
Check out the MCE Optibay alternatives thread on macrumors.com:
http://forums.macrumors.com/showthread.php?t=680228&page=40
Answer: Yes, OWC sells one that can be purchased in a bundle with the Data Doubler. MCE also bundles one with their Optibay product.


Physical Object Detector

Question: Is there a device like barcode reader which detect physical objects with webcam or something like that? I am using a barcode reader for a supermarket and my barcode reader can't read some of the barcodes. My barcode reader is fine, the problem is with my stuffs' barcodes. Is there a hardware or even software to detect the whole objects for me?
thanx in advance
Comment: you might also want to check if rfid tags are the thing for you: http://en.wikipedia.org/wiki/Radio-frequency_identification
Answer: Take a look at SnapTell.  You can take a picture of an object, and they can find a match in a database.  It's pretty amazing.  It's all proprietary, but maybe they'll license their service.
Answer: Object recognition is a very complex field. Although what youa re looking  this is possible i doubt if they are commercially available. If even if it were available it would be really expensive..
Answer: There is a commercial product available that is built to look underneath shopping carts and identify the merchandise by sight.  It's called LaneHawk and is made by Evolution Robotics.

Physical Object Detector


New User limitations

Question: How long does it take to NOT be considered a 'New User'. Is it reputation, day/hour based?
Answer: None of these answers are really correct. There are special limitations for Rep 1 users.
See
What are the limits and restrictions for new users?

New user (less than 15 rep) restrictions:

new users may not post images
new users may only post one URL

New user (less than 100 rep) restrictions:

new users may only post one question every 20 minutes
new users may only post one answer every 2 minutes

To lift these restrictions, gain more rep!
Comment: Just a suggestion, but perhaps these could be included in the FAQ under "What is reputation?" When I first started, I carefully looked up all the URLs in a reply - then found I couldn't post it. Having this in the FAQ would have decreased my frustration.
Comment: In addition to this, [new users (less than 15 rep) cannot mark their questions as community wiki when they initially ask them](http://meta.stackexchange.com/questions/49745/why-cant-i-mark-a-question-as-community-wiki-on-so-when-asking-it/49748#49748).
Comment: I'm wondering if it is less than 100 rep or less than or equal to 100 rep?  I just tried to post two questions in row and was informed I am a new user (pretty accurate :D ) and have to wait 20 minutes. I have exactly 100 rep.
Answer: It is reputation based.  See "What is reputation?" in the faq.

Amass enough reputation points and
Super User will allow you to go beyond
simply asking and answering questions:
15  Vote up
15  Flag offensive
50  Leave comments
100  Vote down (costs 1 rep), create new tags
200  Reduced advertising
250  Vote to close or open your questions
500  Retag questions
750  Edit community wiki posts
2000  Edit other people's posts
3000  Vote to close any questions
10000  Delete closed questions, access to moderation tools
At the high end of this
reputation spectrum there is little
difference between users with high
reputation and moderators. That is
very much intentional. We don't run
Super User. The community does.
Answer: The limit goes away once you hit 100 reputation
Answer: Reputation, I believe. I had that limit this morning (1 question per 20 minutes) and it went away as my reputation increased.
Comment: @Jonathan, this is hilarious now that you have 18k rep (and yes, I know this comment will eventually itself be dated).
Answer: I'm still a "new user" and I've been using this site for seven months. Essentially, you're a new user until a bunch of people get together and decided to vote you up. I know... It really has nothing to do with new, but like most bugs no one seems to care to fix it.
Comment: Evan, your account is very unusual. For 99.999% of accounts this is not an issue.
Comment: @Evan ... I proclaim that, You are *special*.
Comment: @Earlz: why? You would get one too.
Comment: @Jeff s/your account is/you are
Comment: @Jeff I propose a new three diamond user type just for @Evan

New User limitations


Why don't airlines have in-flight video recordings like buses do?

Question: That way we could study plane crashes more closely, or terrorist hijackings, or resolve passenger disputes. Even buses in Ecuador have video cameras.(WARNING: shocking video)
Comment: weight and costs, a passenger can't really disappear after beating someone up on a plane like they can on a bus
Comment: That YouTube link is shocking and disturbing !
Answer: Many airlines do in fact have inflight camera feeds for Cabin surveillance so I do not think the question is relevant to most major airlines anymore.
For a specific example, Emirates Airline employs the Cabin Video Monitoring Systems (CVMS) across its fleet of Airbus A380 aircraft. These Cabin cameras can be accessed by Cockpit crew through the System Display or the Cabin crew through the FAP (Flight Attendant Panel) and for any abnormal situation such as a hijacking/hostage situation on ground, the CVMS can be accessed on a laptop via the GSP (Ground Service Panel). Additionally, as mentioned above, they have landscape cameras installed for an external video feed but that is more of a feature for passengers.
The advantages of a CVMS in a hijacking/hostage situation such as positioning, identity, body language and weapons of the hijackers plus general operational advantages such as issues during boarding/offloading and other emergency situations such as an evacuation are great and not to be discounted.
Comment: It's not clear from your post whether video from the existing cameras is recorded (which is part of the question).
Answer: Regarding cabin cameras, there's not much of a need for them. Busses typically don't have flight attendants. In-flight disputes are typically handled well and quickly by the cabin crew on an airliner. Also, theft or assault would have dozens to hundreds of eyewitnesses and no route of escape for the perpetrator, unlike on a bus (which is probably why such incidents are almost completely unheard of on airliners.) In the case of a terrorist hijacking, having video wouldn't really help much. It's usually pretty obvious when an airliner has been hijacked, but there's not a lot that people on the ground can do about it, aside from the possibility of shooting it down if it appears to be threatening a 9/11-style attack.
Regarding exterior cameras, these are actually starting to appear on some airliners now. Newer airliners like the 777-300ER and the A380, for instance, have them, though I don't think they actually record the video. Even if they did, it seems unlikely that they'd provide any useful information beyond what the FDR data and accident scene examination had already revealed (i.e. they'd basically just show that the plane ran into the ground, which would already be known by the time you found the video.)
Regarding cockpit video recording, there is an answer here that addresses it. There have been some suggestions for this to be added over the years, but pilots tend to be against it and the additional information it would provide would likely not be particularly useful in most instances, given that we already have a recording of all of the conversations up to the time limit of the recorder as well as the FDR data.
Comment: @DavidRicherby Good point. I meant all of the conversations taking place while they're recording (i.e. radio calls as well as conversation between the crew members,) but you're right that the time duration is limited. Normally the last two hours would be plenty to capture everything relevant to an accident, but MH370 is indeed a notable example where it likely wouldn't be. These days, one would think it would be trivial to remove that duration limit, though a new design would have to be recertified.
Comment: Note that cockpit voice recorders *don't* give you a recording of all conversation: they give you a recording of all conversation in the (typically, as I recall) two hours before they were switched off. So, for example, the CVR from MH370 is ever found, it will probably be no use, since the plane flew on for hours after it changed route, so the critical conversations will have been overwritten multiple times.
Comment: CVMS (Cabin Video Monitoring Systems) can definitely help in a hijack situation on ground to aid authorities in establishing various attributes related to the hijacking situation. This information may include 1) Identities 2) Positions 3) Weapons 4) Body Language 5) Others. There's a reason why many airlines employ such systems.
Comment: @Kamran OTOH, every system has to have a fuse, and the hijackers may easily know how to switch it off.
Comment: @yo' Of course there are lot of components that can be damaged by any hijackers but that goes for any security measure, nothing is 100% secure. The balance of probability suggests that it will be very difficult for anyone to disable this particular system (Or others configured like it). The power for the CVMS (Cabin Video Monitoring System) can also be through the GSP when the laptop is connected for external viewing. Additionally, the access to the CB's (Circuit Breakers) would be through the Avionics Bay which is accessible from the Cockpit, Externally or the Forward Cargo Compartment.
Answer: Note that cameras are already installed in some aircraft; but I believe this is an operator option and not standard equipment.
For example, from this incident report of a 737-800 PDF:

The captain stated that he could see on the cabin observation camera
  screen in the cockpit that a CCM was wearing personal breathing
  equipment (PBE). The captain switched off the IFE. This action also
  switched off the camera since the IFE and the camera are on the same
  electrical bus.
Answer: You will see them very soon. Actually, I have already made the software for that :) and we will be delivering to few of the Airlines very soon as I work on those systems where we will have the DVR (Digital Video Recorder) and and a live streaming panel. This recording is only manually controlled just by push of a button by pilot or crew. You will see them in B787s. There are few in A350 also for few airlines.
Comment: A lot of airlines already use Cabin Video Monitoring Systems and already have live display on the Flight Attendant Panels. The software(s) already exist for such systems are in use for various aircraft belonging to various airlines.


How is charge dissipated in ion-propulsed spacecraft?

Question: I understand that an ion-thruster will continuously charge its spacecraft with a charge opposite of the one of the ions it thrusts. Over a long journey this charge would be considerable. What would happen when such a spacecraft comes in contact with another celestial body? Do engineers need to come up with a mechanism to dissipate the charge in a controlled manner?
Answer: Equalizing the charge of an ion thruster is a real problem. It is not possible to eject only positive xenon ions over a long time. The space craft would charge negatively and ions would be "pulled back" to the spacecraft.
To avoid this, also negative electrons are ejected to neutralize the spacecraft and the ion beam. There is a special electron ejector besides the ion ejector. The sum of the related electrical currents of charged ions and electrons should be zero to avoid a increasing charge of the spacecraft over time.
See Why are Ion Thrusters so energy hungry? for a picture of an ion thruster with the electron injector.
Answer: Ion drive spacecraft need to eject a net neutral amount of charge. Otherwise, the spacecraft would become so charged that the ion exhaust would just be sucked right back to the spacecraft. It takes an absurd amount of voltage to charge something by only a small net amount of missing ions.
Neutralization is done by mounting electron emitters on the spacecraft, which operate while the ion drive operates and spray an equal amount of electrons in roughly the same direction as the ion drive exhaust.
These may be simple hot-filament cathodes much like those in vacuum tubes and electron microscopes, or a variety of other designs including ones that operate on the cold-cathode principle.
Comment: I don't know why someone down voted, but this would become a wonderful answer if you could cite or link to a few specific examples!


Which chapters of the manga do the season 1 and 2 of the Mob Psycho 100 anime cover?

Question: I'm currently watching Mob Psycho 100, the last episode of season 2 was Mob fighting Keiji Mogami. Which chapters of the manga do the season 1 and 2 of the Mob Psycho 100 anime cover?
Comment: "Last" as in "most recent"? Because season 2 is still airing...
Comment: The first season covers about the first 6-6.5 volumes. There are 16 volumes in total, so depending on how the stuido planned it second season might or might not adapt the remaining 9.5-10 volumes
Answer: Season 1 covers Volume 1 through 6. Season 2 will most likely cover Volume 6 through 13.
Season One ends on Chapter 50 ("No Changes") but also includes an omake chapter ("Romance and Impulse".) at the end of the episode.**
Season Two has covered Chapter 51 through 91.


Retrocausal interpretations of quantum mechanics

Question: Can retrocausality resolve the paradoxes of quantum mechanics? The Copenhagen interpretation presumes something has no property until it is measured, but retrocausal interpretations explain that away by claiming that thing has a definite property before measurement, but the choice of which property is affected by the configuration of the measuring apparatus in its future. The philosopher Huw Price has written a lot about this. Nonlocal entanglements are also explained away because entangled pairs are connected by going to the past, then back up to the future. Or going to the future, then back to the past without travelling faster than light at any time.
Comment: Related: http://physics.stackexchange.com/questions/3767/the-transactional-interpretation-of-quantum-mechanics
Answer: Not "resolve". Give an interesting account, perhaps. This kind of interpretation suffers from the usual problem for interpretations, that it doesn't add enough that is useful enough for many Physicists to have wanted to use it, at least in the relatively elaborated form proposed by Huw Price. On the other hand, understanding this kind of interpretation and its position relative to other interpretations of quantum theory is essential to anyone working on the Philosophy or Foundations of Physics. It's also notable that backward trajectories do appear in some readings of Feynman diagrams, which could be said to make this kind of interpretation rather mainstream, however I would say that Physicists' use of this kind of language is not quite enough to justify calling it an interpretation.
Explaining "nonlocality" by introducing "backward propagation" could well be said to be no explanation at all. Neither concept is exactly classically intuitive, for example. Nonetheless, we can hope that understanding that a tradeoff can be made between nonlocality and backward propagation is worthwhile.
Answer: initial state: a pair of electron and a positron moving toward each other
A pair of electron and a positron have certain probability of annihilating to each other in certain amount of time, the resulting photon amplitudes are described by some Feynman diagram (the sum of all Feynman diagram with the same In and Out states of course)
In this case we could interpret the electron as bouncing from a backward propagating photon, and becoming a backward propagating electron (a positron), but such interpretation is pointless because of conditional probabilities and entanglement
Let me explain that last phrase above: the initial state assumes that i've already make measurements which couple me (the observer) to a definite state at time $t_0$, so, if i accept that any retrocausal interpretation needs to produce consistent histories (i.e: if i measure A at $t_0$, i always will measure A at $t_0$, regardless of what happens before or after) then all probabilities can only define what happens at other times that are not $t_0$, and such probabilities are given by propagators and a well known state at $t_0$.
so, i hope to have made clear from the above paragraph that before we can speak consistently of any "retrocausality", we need an alternative way to represent dynamics evolutions to the usual propagator which assumes 100% knowledge of state at $t_0$ and produces amplitude probabilities of states at $t_1$. So we need some formalism that might take a partial state at $t_0$, compute amplitudes at another partial state at $t_1$, then from making measurements at both times, and measure correlations (which could be interpreted in principle as entanglement correlations nonetheless) one could infer that a definite result at the measurement in $t_1$ changed part of the state at $t_0$ that was unknown to us, but it obviously had to be measured by a separate apparatus in order for us to measure such a correlation
It should not be a surprise that even if we had such a formalism, it would only differ from the Propagator formalism in the interpretation. I could still assume that the state at $t_0$ was perfectly known, only by different apparatuses, and the propagator produced the observed amplitudes at $t_1$
the whole "retrocausality" concept becomes non-trivial only if there are fate conditions, that is, boundary conditions in the future that are unavoidable (for example, imagine a universe with a entirely time simmetrical big-crunch, where the universe seems to have an arrow of time in the first half, but when approaching the half life of the universe, matter slowly starts becoming antimatter by seemingly random fluctuations). Our current universe does not manifest any such flagrant violations of the second law, so the concept of retrocausality is not useful to model physics.
Answer: The ordinary Retrocausal interpretation of quantum mechanics, was Cramers transactional
interpretation, where an event is formed as a single point in space time, where an incoming
wavefunction from the past, and an incoming (advanced wave) wavefunction from the future meet.
The theory has a fixed past and future points, which can then predict observation in the
time between. It remains mathematical correct, but of course is hardly useful for predictions.
Interesting to me, is between an transactional interpretation with one fated future, and a many worlds interpretation with all possible futures, are there any conditions which would allow us to removed possible futures, or truncate the calculation of probability amplitudes at low levels of likelihood.
Answer: Retrocausal interpretations may explain Bell inequality violations for entangled particles and delayed-choice experiments, but can retrocausality explain how quantum computers can factorize large integers or compute discrete logarithms using Shor's algorithm? Even if retrocausal effects exist, they can't constitute a complete account of quantum mechanics.


Can I protect a french polished finish with laquer?

Question: I am making a dining table out of walnut which is highly figured.  What is the best finish so that the table can be used?  I know French Polishing it will really enhance the timber but it seems so fragile and prone to damage, so I wonder if there is anything you can do to protect it and make it more durable and user friendly?
Comment: Even if it is true that French Polishing produces a better result than modern varnishes by giving greater chatoyancy (or whatever), wouldn't varnishing over the shellac undo that advantage?
Comment: Have to ask, have you French polished before? If not I wouldn't expect to get an acceptable result first time, it's considered a *very* challenging finish to pull off. Now besides that, I think you'll find if you do a quick comparison test that the shellac doesn't give a finish superior to varnish used straight on the wood!
Comment: Thank you - I have French polished a sideboard with a good result, but it is VERY challenging I agree.  I might do some tests on some offcuts - thanks for the suggestion.
Answer: You may be able to with the right lacquer (or "lacquer") but you probably don't have the expertise and equipment to apply one to the necessary standard. But that's OK because you can do what you want with polyurethane varnish and that is easily applied to a high standard by thinning it and applying it as wiping varnish.
See previous Answer for more on wiping varnish.
Comment: Did you mean 'lacquer or ("laquer")'?  At the moment, I can't make sense of your parenthesised alternative.
Comment: @MartinBonner The parenthetical comment is to refer to products named lacquer which aren't actually lacquer, at least not in the conventional sense. I similarly use quotes for other product names like "gel stain" and "Danish oil" where the words don't accurately describe what you're buying.


Why do some minifigs have yellow heads and some are flesh colored?

Question: When did the flesh colors start and why? It seems yellow heads are here to stay too?
Comment: I remember back in the old LEGO Club days, there was a guy called Redini who would answer questions by club members. One of them asked a similar question, except phrased more simply: "Why are LEGO people yellow?" While the old LEGO Club site is nowhere to be found, forum posts from the same era quote his relevant answer verbatim... not sure if I should bother quoting it as an answer here since it was answered way before more minifig head colors appeared.
Answer: To answer the first part of the question, the Company Profile presentation (deep, direct link) states:

When the minifigure first appeared, it was decided that its face should have only one colour: yellow. And that its facial features should be happy and neutral . The figure would have no sex, race or role – these would be determined by the child's imagination and play.

It then explains when and why they added colour for their licensed figures

With licensed products such as LEGO® Star Wars™ and LEGO® Harry Potter™ the figure began appearing in specific roles, and with LEGO Basketball in 2003 it took on authentic skin colours. In 2004 the LEGO minifigure assumed an even wider range of skin colours when it was decided that the figures in licensed products should resemble the original characters as closely as possible. One result was that the figures in LEGO Harry Potter™ changed from yellow to a more authentic skin colour.

The first ones I remember seeing were indeed some of the NBA League characters as part of the Basketball theme in 2003, followed by the Star Wars products and then the Harry Potter sets in 2004.
Lando Calrissian was one of the first to appear in the correct skin tone, amongst yellow Han and Leia:

Followed later by pink characters for the rest. The first Star Wars set in 2004 with flesh-toned figures was the Millennium Falcon. By 2005 the transition for Star Wars was complete and all sets used flesh-toned figures.
In terms of other colours, LEGO had already created various monster and alien figures with different coloured heads ranging from blues and greys through to transparent and even transparent neon orange.
Comment: Clarification: non-human and monstrous minifigs had non-yellow heads long before the flesh-toned heads, however, they usually aren't Caucasian-skin-peach-toned.
Comment: @Mr.ShinyandNew安宇 Updated ;)
Comment: The answer is very good, but at its level of detail, one somehow also expects a citation related to the fact that yellow is kept as the default skin colour in non-licensed sets. After all, the other decisions from the original minifigs quotation *have* been revised in the meantime (gender already a long time ago, first by clothes and hairstyles, then by printed heads with red lips; and the bit about a neutral or happy facial expression stopped being completely true when the two-sided heads with a "panicked" expression were introduced).
Comment: Cheers, if you have a citation beyond what was in the company profile clearly states (as quoted) "it was decided that the figures in licensed products..."
Answer: The Cult Of Lego book (ISBN: 978-1-59327-391-0) had an a whole page about the change in minifigure skin colour:

Page 59, sentence 2:
  Originally, the LEGO Group sought to leave racial and gender
  differences to the imagination of builders by using a stylised,
  generic face with outfits to differentiate roles.
Page 59, sentence 4: The most noticeable feature of the majority of mini-figs is
  their ostensibly "race-neutral" yellow coloration. The paradigm lasted until
  2003, when LEGO Sports' Basketball theme was released, featuring
  minifigs based on real-life NBA players. The LEGO Group decided that
  expecting kids to appreciate figures that didn't really resemble the
  stars they represented was a losing proposition.

Since the NBA figures were released in 2003, beige and brown skin tones have been used only in licensed sets to portray characters. Traditional LEGO themes like Police and Firefighters continue to use a yellow flesh colour.
The distinction between skin tones makes it easy to identify a beige or brown minifigure as part of a licensed set. Licensed sets tend to be based on film and television themes.
Answer: Licenced Themes, use skin tone heads since they are based on something. Themes that LEGO Made themselves, such as Creator have yellow heads.
Answer: The yellow head was originally used to represent all races and both genders. Later, yellow heads were used to represent non-licensed minifigures, and flesh coloured minifigures were used to represent licensed minifigures, such as Batman, or Indiana Jones, but flesh coloured minifigures weren't used until around 2003
Answer: I think the flesh colored ones are reserved for Minifigures made in an actual characters'  likeness, and the yellow is reserved for generic figures.
Comment: This answer doesn't seem to add anything beyond what other answers have already stated.
Answer: Flesh colored is used for licensed brands, such as Star Wars and Jurassic World.
Comment: This answer doesn't seem to add anything beyond what other answers have already stated.


Can I fast without sehri (suhoor)?

Question: In the month of Ramadan, what should a person who couldn't wake up for suhoor do? Should he continue the fast or should he compensate for it later?
Answer: Eating Suhur is Sunnah. Not obligatory. As Prophet Muhammad (Salla-Allahu-Alaihi-Wa-Sallam) Says,

"Eat Suhur (predawn meal). Surely, there is a blessing in Suhur."

Source: This hadith from Bukhari and Muslim
But, Keeping Fast during Ramadan is Obligatory for every Muslim. As described in the Quran and many Ahadith of Prophet (Salla-Allahu-Alaihi-Wa-Sallam).
The Ayat from Quran is

The month of Ramadhan [is that] in which was revealed the Qur'an, a guidance for the people and clear proofs of guidance and criterion. So whoever sights [the new moon of] the month, let him fast it; and whoever is ill or on a journey - then an equal number of other days.

Source: Sahih International Translation of The Holy Quran
So, the conclusion is, Even if you missed Suhur, You have to fast. Suhur is not obligatory and it is a Sunnah and Prophet says, there is Barakah (blessings) in Suhur. But, it is not in the per-requisites of Fasting
Hope this will help
Answer: All the other answers (correctly) point out that fasting is wajib (obligatory) and suhoor is sunnah (in the sense that it is not obligatory, but recommended). However, more clearly, the reason you still have to fast is because of the conditions of fasting:

Being Muslim
Being beyond puberty and possessing a sound state of mind
Having the ability to complete the fast
Not being sick or in a state of travel
Not having other impediments to fasting (women in their menses etc.)

As you can see, suhoor is not a condition for fasting - and therefore you are obliged to fast despite missing suhoor. If one of the conditions is broken, only then you are not obliged to fast.
So while the wajib/sunnah distinction is valid, technically it would be that suhoor is not a condition for fasting that gives you the answer to your query. And Allah knows better.
Source for conditions of fasting
Comment: @Mr.TAMER Akhi they are the same thing - only the Ahnaf differentiate between the two, and that difference doesn't affect the ruling, only the derivation.
Comment: fasting ramadan is not wajib, it's Fardh.
Comment: Great question: what is the exact difference between the two.
Comment: @ashes999 Asked and answered: http://islam.stackexchange.com/q/852/18
Answer: You can and you must!
There is no excuse of breaking the fast if you skipped Sehri for one reason or another. Sehri (mid night meal) has it own benefit and is recommended by the prophet but that is not a requirement for fast. All you need to do is make your intentions for fast and offer prayer. The prayer is
'Wa be somi ghadin navaithu min sheri ramadan' meaning
" I have made the intention of obligatory fast for this day of Ramadan for the sole pleasure of Allah Almighty."
Intention for fasting

The time for the intention (Niyyat) for fasting begins anytime after
  sunset until midday. Intention is obligatory and it is Sunnat to
  recite it verbally each day. Even if the intention is made before
  midday the fast will be valid. Recite Durood Shareef before and after
  making the intention.

So in short sehri is not compulsory for fasting but it is highly recommended. If you skip it which can very well happen, you should still keep the fast.
If you skipped sehri and now it is too hard for you to keep the fast, that is probably another question.
Answer: As othe answers mentioned, suhoor is a Sunnah (and a recommened Sunnah), but it's not obligatory, and many people don't take it when the fast-time is short and the eating-time is long, however it's still recommended to take it, as this Hadith mentions:

Anas (May Allah be pleased with him) reported:
The Messenger of Allah (PBUH) said, "Eat Suhur (predawn meal). Surely,
there is a blessing in Suhur."
[Al-Bukhari and Muslim].
عن أنس، رضي الله عنه قال: قال رسول الله صلى الله عليه وسلم:
"تسحروا فإن في السحور بركة"
متفق عليه))
Riyad as-Salihin

So you see that suhoor is a confirmed sunnah, but it's still Sunnah, not obligatory, not taking suhur:

Neither spoils your fasting: You still can fast if you have the intention.

Nor give you permissions to eat after fajr (the starting time of fast), as this fasting duration is mentioned in Quran and eating anything within that duration breaks your fast:

أُحِلَّ لَكُمْ لَيْلَةَ الصِّيَامِ الرَّفَثُ إِلَىٰ نِسَائِكُمْ ۚ
هُنَّ لِبَاسٌ لَّكُمْ وَأَنتُمْ لِبَاسٌ لَّهُنَّ ۗ عَلِمَ اللَّهُ
أَنَّكُمْ كُنتُمْ تَخْتَانُونَ أَنفُسَكُمْ فَتَابَ عَلَيْكُمْ وَعَفَا
عَنكُمْ ۖ فَالْآنَ بَاشِرُوهُنَّ وَابْتَغُوا مَا كَتَبَ اللَّهُ لَكُمْ
ۚ وَكُلُوا وَاشْرَبُوا حَتَّىٰ يَتَبَيَّنَ لَكُمُ الْخَيْطُ
الْأَبْيَضُ مِنَ الْخَيْطِ الْأَسْوَدِ مِنَ الْفَجْرِ ۖ ثُمَّ
أَتِمُّوا الصِّيَامَ إِلَى اللَّيْلِ ۚ وَلَا تُبَاشِرُوهُنَّ وَأَنتُمْ
عَاكِفُونَ فِي الْمَسَاجِدِ ۗ تِلْكَ حُدُودُ اللَّهِ فَلَا
تَقْرَبُوهَا ۗ كَذَٰلِكَ يُبَيِّنُ اللَّهُ آيَاتِهِ لِلنَّاسِ
لَعَلَّهُمْ يَتَّقُونَ
Sahih International
It has been made permissible for you the night preceding fasting to go
to your wives [for sexual relations]. They are clothing for you and
you are clothing for them. Allah knows that you used to deceive
yourselves, so He accepted your repentance and forgave you. So now,
have relations with them and seek that which Allah has decreed for
you. And eat and drink until the white thread of dawn becomes
distinct to you from the black thread [of night]. Then complete the
fast until the sunset. And do not have relations with them as long
as you are staying for worship in the mosques. These are the limits
[set by] Allah , so do not approach them. Thus does Allah make clear
His ordinances to the people that they may become righteous.
[Surat Al-Baqarah:187]

As you see Quran explicitly says that you can eat till fajr time, and after that you'll have to fast until Maghrib.
Hope that's helpful.
Answer: Yes. You can be fasting without eating sahari. Having sahari (eating food before Azan of Fajr in order to being with sufficient energy as much as possible during the day before you want to be fasting). In other word, perhaps Islam recommend muslims to eat sahari before fasting, in order to being able to bearing it during the day, otherwise it would be very difficult for everyone in order to bear it without sahari. So it indicates that how much Islam is paying notice to muslim programs. But islam has not pointed it out as a wajib act. Then you can.fast without waking up at the sahari.
Answer: Of course you should fast even if you miss suhoor. Kids above 12 years must fast. Anybody younger who couldn't take hunger don't have to fast. But when they do suhoor they should fast.
Suhoor is a Sunah. You must fast if you eat at that time. Fasting is mendatory for anybody at a puberty age (12+ years).
So even though you miss suhoor, if your 12+ years, you must fast at all costs.
Comment: -1, if you are an adult, then you should fast. And the definition of an adult in Islam is someone who reached puberty which differs from one person to another. Someone who lives in desert reaches puberty at age of 9. Thus, he/she should start fasting at the age of 9.

Can I fast without sehri (suhoor)?


How to preserve fermented bean sauce

Question: How can I can and preserve my fermented bean sauce so it has a long shelf life preferably one year or longer. I ferment the beans in smoke and in low heat and then stir fry them in mustard oil, garlic, sesame seeds, turmaric, salt and ginger. I am the only one in the house who eats this yummy smelly sauce. If I can't prolong its shelf life I will have to throw away a lot of it.
Thanks
Comment: Someone else will come along to advise about canning, I don't know much about that. I *do* know that you can freeze it. How much sauce do you need to preserve? Do you have the freezer space? If so, I'm happy to give you advice on how to do it well.
Answer: not sure what you mean by 'fermenting in smoke'. Fermenting is generally accepted as being encouraging natural lacto-bacillus production in the food by using brine and controlling the temperature of your jar or crock within a certain (coolish) range for days/weeks. This process preserves the food to an extent, but must then be kept in the fridge which slows down decay but doesn't halt it like pickling in vinegar, canning or freezing food does. A tip with fermented foods is that the significant health benefits are lost if you heat them, better to add them on top of heated food at the end.
If what you're actually doing is smoking (rather than fermenting), then shelf-life will depend on a) whether it is a cold smoking or hot smoking process you are using; b)how long you are smoking for and c) how you store it (under oil, in a sterile jar, etc).

How to preserve fermented bean sauce