What is Android's sleep mode Many developers speak of Android's sleep mode. 

When exactly the device goes into sleep mode ?

What is st standby mode ?

How standby and sleep mode are different (or related)?

When the device goes to standby ?

What are the factors deciding whether standby or sleep mode ?

Is there any thing called deep sleep ? (or deep standby), If so, info on it please...

What services are shut down in sleep mode ?

What will happen to the shut services on device wakeup.

Consider I am downloading a file using ES Downloader, and gives the hide option.

Say it's a huge file like 100mb,
CASE 1 :
My device screen dims, then screen turns off, but not locked.
CASE 2 :
My device screen dims, then screen turns off, and it goes to locked state.
A few to much questions for a single post, though they are mostly related. Let's roll up from the end:

Deep Sleep is a state where the CPU has "nothing to do at all". Depending on the tasks the device has to perform, CPU runs in different "speeds" (frequencies). Say you've got a 1 GHz CPU, that doesn't mean it permanently runs at 1 GHz (and eats your battery); it will only "fully power up to that" if there is demand for it. On average, it will run on much lower frequencies, down to ~50 MHz. If there's really nothing to do, the system will "send it to sleep", and set a timer to wake it up later. This state is called "deep sleep".

Your device goes to Standby only when you've turned the display off, never when the display is turned on. IMHO "Standby" and "Sleep mode" are synonyms. But switching off your display is not the only criterium for entering Standby. Depending on your device's settings and apps currently started/running, e.g. running downloads might continue, as well as other "ongoing calculations". The "locked state" usually has nothing to do with it: that's rather a "security measure" against "unwanted access".

What services are stopped when you switch off the screen is something no generic answer can be given to: this very much differs not only between devices and Android versions, but also depends on what apps you have installed and how they're programmed/configured.

As for your specific example: This again depends. Say you've switched off mobile data, and run your download on WiFi. Your "WiFi Standby Policy" is set to cut the connection when the screen is turned off. Results for your download should be obvious then :)



Note that this answer most likely is incomplete, as the topic is rather complex – and your number of questions don't make it easy to answer in a short manner.