The M9900 64K RAM board was a high speed random access read/write memory
board designed expressly for use with the M9900 CPU. It uses
industry-standard 16K dynamic RAM circuits to achieve its goals of high
speed, reliability, low cost, and minimal power consumption. The 64K RAM
board operated with the M9900 CPU at either 2 Mhz or 3 Mhz, with fully
transparent refresh which guaranteed reliable data storage without imposing
a speed penalty on the CPU. The M9900 64K RAM took advantage of the M9900
CPU's 16 bit data transfer mode. This mode permited the CPU to transfer data
on a word by word basis rather than the normal 8 bit byte transfers used by
some other S-1OO memories. Use of a 16 bit transfer and the elimination of
redundant bus cycles allow memory transfers to be completed in one third the
time when the M9900 64K board is being accessed, as compared with
conventional S-100 memories. This results in an overall doubling of system
performance when the M9900 64K board replaces regular S-100 memories.
The M9900 64K RAM features programmabe memory management hardware. Pages of
memory on the board could be enabled and disabled in 4K byte increments. The
initial configuration of the board is set bv switches on the board, and the
memory map may be changed at any time by software. When used in conjunction
with the Marinchip Multi-User Network Operating System (NOS/MT), this allows
system memory configurations as large as 16 megabytes.
The manual for this board can be obtained
here.
