chap file processing and external sorting takes maximum advantage of this micro-parallelism is double buffering imagine that file is being processed sequentially while the first sector is being readthe cpu cannot process that information and so must wait or find something else to do in the meantime once the first sector is readthe cpu can start processing while the disk drive (in parallelbegins reading the second sector if the time required for the cpu to process sector is approximately the same as the time required by the disk controller to read sectorit might be possible to keep the cpu continuously fed with data from the file the same concept can also be applied to outputwriting one sector to disk while the cpu is writing to second output buffer in memory thusin computers that support double bufferingit pays to have at least two input buffers and two output buffers available caching information in memory is such good idea that it is usually extended to multiple buffers the operating system or an application program might store many buffers of information taken from some backing storage such as disk file this process of using buffers as an intermediary between user and disk file is called buffering the file the information stored in buffer is often called pageand the collection of buffers is called buffer pool the goal of the buffer pool is to increase the amount of information stored in memory in hopes of increasing the likelihood that new information requests can be satisfied from the buffer pool rather than requiring new information to be read from disk as long as there is an unused buffer available in the buffer poolnew information can be read in from disk on demand when an application continues to read new information from diskeventually all of the buffers in the buffer pool will become full once this happenssome decision must be made about what information in the buffer pool will be sacrificed to make room for newly requested information when replacing information contained in the buffer poolthe goal is to select buffer that has "unnecessaryinformationthat isthat information least likely to be requested again because the buffer pool cannot know for certain what the pattern of future requests will look likea decision based on some heuristicor best guessmust be used there are several approaches to making this decision one heuristic is "first-infirst-out(fifothis scheme simply orders the buffers in queue the buffer at the front of the queue is used next to store new information and then placed at the end of the queue in this waythe buffer to be replaced is the one that has held its information the longestin hopes that this information is no longer needed this is reasonable assumption when processing moves along the file at some steady pace in roughly sequential order howevermany programs work with certain key pieces of information over and over againand the importance of information has little to do with how long ago the informa