DEADLINE DRIVEN DISK SCHEDULER METHOD AND APPARATUS WITH THRESHOLDED MOST URGENT REQUEST QUEUE SCAN WINDOW

A disk control mechanism for controlling the operations of a movable arm disk drive. The disk control mechanism contains a disk access scheduler which accepts disk access requests having a deadline and a disk location. The disk access scheduler further consists of a queue data structure for storing the requests. The queue contains a predefinded window that contains a certain number of requests with deadlines to expire sooner than all other requests. The request that is most soon to expire, the most urgent request, is located at the head of the queue. The disk access scheduler contains logic to determine whether the most urgent request has a deadline to expire sooner than tolerated by a set threshold, and in such cases the disk access scheduler schedules for service the most urgent request prior to any other request, otherwise it scans towards the most urgent request and schedules requests with a disk location between the current arm location and the most urgent request.