AT&T PC 6300 - Memory

SYSTEM OVERVIEW P[
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Memory
2-16
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The Motherboard RAM is organized in such a way that it can be
addressed as bytes (8 bits) as well as words (2 bytes/16 bits). It is
divided into two banks: bank 0 and bank 1. Both banks have two W
groups of nine 64-K or 256-K bit chips. One group is the lower j J
byte (even address) and the other is the higher byte (odd address).
Eight chips of each group are used for memory storage and the _
ninth chip is used for parity checking. All RAMs are dynamic and j j
require periodic refresh. Memory refresh is provided by the DMA
circuitry.
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The Motherboard has four standard memory configurations:
128 KB, 256 KB, 512 KB (CPU 3X), and 640 KB. In the 128-KB
configuration, the RAM resides in bank 0. Initially, bank 1 does M
not contain any memory chips, but sockets are present for the easy
expansion of the Motherboard memory. With the insertion of
64-K bit memory chips into bank 1, the Motherboard memory is
expanded to 256 KB. With the insertion of 256-K bit memory chips
into bank 1, the Motherboard memory is expanded to 640 KB. In
the 256-KB configuration, both banks 0 and 1 may be soldered to
the Motherboard. The 64-K bit chips in one of the banks can be j
replaced with 256-K bit chips that will provide 640 KB of RAM on -
the Motherboard.
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