Method for Reducing Path Length for Sequential I/O Processing
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
By looking at the next element on the queue before the previous element is dequeued, the timing requirement of a disk drive is met so that revolutions of the disk are minimized for sequential I/O operations. In a UNIX* system environment, data requests occur mostly in 2K blocks. In the case of UNIX exec loading, these 2K blocks will be exactly sequential. It is required when loading data sequentially that no extra revolutions of the disk occur. This forces the disk device driver to complete an active request and start the next request within a time of 975 microseconds. Of this time, the hardware takes 465 microseconds. This allows the device driver only 510 microseconds. Additionally, new requests are given to the device driver only upon completion of the previous request.