Abstract: Translating between physical and logical (or virtual) address spaces occurs autonomously using information decoded by an address mode translator from command bits within a host CPU issued command. The translator communicates with a hard disc controller unit local microprocessor or microcontroller and controller unit task registers. A host CPU issued command interrupts the local microprocessor and activates the address mode translator by writing to an appropriate controller unit task register using indirect addressing. The address mode translator preferably provides four algorithms, with algorithm selection occurring autonomously according to the decoded command bits. The algorithms provide physical block address to physical CHS cylinder-head-sector conversion, logical CHS to logical block address conversion, and also provide divide and multiply functions, useful for disc caching.

Abstract: A disc controller services a host "read" command, without intervention by the disc controller's microcontroller, if the requested data is found in the disc controller's cache. The disc controller stores at least one cache entry. Each cache entry includes an address, a logical Bit, a valid Bit and a set of four buffer parameters: upper limit address, base address, pointer to the sector count and sector count. Each host command is decoded by the disc controller, and if the command is a "read" command the address in the cache entry is compared against the address in the host command. If the addresses match and the cache entry address is marked as being valid by its Valid bit, a "cache hit" signal is generated and the disc controller starts transferring the data requested by the host without waiting for the disc controller's microprocessor to process the host command.