buffers and buffer pools given the specifications of the disk drive from example we find that it takes about + ms to read one track of data on average it takes about ++( / ) ms on average to read single sector of data this is good savings (slightly over half the time)but less than of the data on the track are read if we want to read only single byteit would save us effectively no time over that required to read an entire sector for this reasonnearly all disk drives automatically read or write an entire sector' worth of information whenever the disk is accessedeven when only one byte of information is requested once sector is readits information is stored in main memory this is known as buffering or caching the information if the next disk request is to that same sectorthen it is not necessary to read from disk again because the information is already stored in main memory buffering is an example of one method for minimizing disk accesses mentioned at the beginning of the bring off additional information from disk to satisfy future requests if information from files were accessed at randomthen the chance that two consecutive disk requests are to the same sector would be low howeverin practice most disk requests are close to the location (in the logical file at leastof the previous request this means that the probability of the next request "hitting the cacheis much higher than chance would indicate this principle explains one reason why average access times for new disk drives are lower than in the past not only is the hardware fasterbut information is also now stored using better algorithms and larger caches that minimize the number of times information needs to be fetched from disk this same concept is also used to store parts of programs in faster memory within the cpuusing the cpu cache that is prevalent in modern microprocessors sector-level buffering is normally provided by the operating system and is often built directly into the disk drive controller hardware most operating systems maintain at least two buffersone for input and one for output consider what would happen if there were only one buffer during byte-by-byte copy operation the sector containing the first byte would be read into the / buffer the output operation would need to destroy the contents of the single / buffer to write this byte then the buffer would need to be filled again from disk for the second byteonly to be destroyed during output the simple solution to this problem is to keep one buffer for inputand second for output most disk drive controllers operate independently from the cpu once an / request is received this is useful because the cpu can typically execute millions of instructions during the time required for single / operation technique that