jhs@MITRE-BEDFORD.ARPA (08/01/87)
L. J. Dickey comments that my RAM-assisted hard disk (the concept obviously HAS to be called a RAMcharger!) is much like cache memory. Good point. But, asymptotically as memory prices go to zero, it may get cheaper to just cache the whole disk than to spend engineering dollars trying to devise faster cache algorithms. Another point in favor of such a design is that the full-sized RAM-hard-disk could be switched into "independent" mode, giving you a full, blindingly fast hard disk for scratch operations like humongous matrix inversions, sorts, or whatever, using normal file structures. When in this mode, accesses to the magnetic disk would be at normal speed. Or, better yet, reserve a few hundred K or so of RAM for a more conventional cache memory, with lower performance. When you were through with the scratch disk operations you could go back to single-drive, "RAMcharged" mode, and ALL hard disk accesses would be fast. I bet we'll see some commercial hard disks using this idea in a few years. Just keep saying to yourself, over and over, "Memory is Free!". -John Sangster, jhs@mitre-bedford.arpa