Abstract: A cache memory is divided into two parts, a master cache memory and a slave cache memory. The slave cache memory receives data from a slow source and then sends it quickly to the master cache memory so that the master cache memory is occupied less of the time with reading or writing data to or from a mass-storage or other peripheral device and is available more of the time for reading or writing data to or from main memory and responding to CPU requests.

Abstract: A zone-bit-recording disk drive has a rotating platter with a surface which is divided into at least two zones each having a respective different number of angularly spaced sectors therein. A method and apparatus for positioning the head relative to the platter surface involve maintaining a count of the number of sectors which pass the head after the platter passes a predetermined angular orientation, ignoring the count during a time interval when the head moves out of a first of the zones toward a second of the zones which contains the specified sector and until the head has entered the second zone and the platter thereafter passes a predetermined angular orientation, and thereafter determining when the count corresponds to the specified sector to be accessed.

Abstract: The invention is an improved method of implementing the "least-recently-used" (LRU) replacement algorithm in a cache memory. Each data block in the cache memory is numbered with a priority tag ranging from 0 to the number of blocks in the cache memory The lowest numbered block is always replaced first. The just replaced block is given the highest priority tag and one is subtracted from each other priority tag. When a requested block is found in the cache, one is subtracted from each priority tag greater than the requested priority tag and the requested block is given the highest priority tag.

Abstract: A method of dynamically prefetching data for a cache memory is controlled by the past history of data requests. If the previous fetch and current fetch request are not sequential, no data is prefetched. If the previous fetch and current fetch request are sequential and less than all of the current fetch request is already in the cache, two blocks of data sequentially beyond the current fetch request are prefetched. If the previous two blocks fetched and current fetch request are sequential and less than all of the current fetch request is already in the cache, four blocks of data sequentially beyond the current fetch request are prefetched. If the previous three blocks fetched and the current fetch request are sequential and less than all of the current fetch request is already in the cache, eight blocks of data sequentially beyond the current fetch request are preferred. The prefetch algorithm is limited at eight blocks.

Abstract: This invention pertains to a disk channel controller for controlling data transfer to and from a disk drive formed of several disks. The controller includes data ports for receiving and transmitting data, head tracking circuits for tracking the heads which store and retrieve data to and from the disks, temporary memories and a microprocessor. Except for the microprocessor, all the controller elements are hardwired. A novel disk formatting is also described.