Zenith Z-100 Series, Reference Manual

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page 6.2
System Memory
General
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The memory cards contain the main user-accessible dynamic RAM and associated
timing and multiplexing circuitry. These cards interface with the system through
one of the parallel I/O connectors located on the backplane board. Connection
with the cards is implemented through the use of a 64-pin edge connector which
is an integral part of the cards. A configuration jumper on these cards enables
up to two blocks (two cards) of memory to be designated as residing in the system.
Specifications
Your computer comes with a minimum of 128 kilobytes of RAM but may contain
up to 640K if additional banks and a second memory card have been installed.
One bank of memory consists of nine dynamic RAM integrated circuits. Eight
of the chips store data, and one chip in each bank is used for a parity check
of stored data.
As presently configured, memory may be added in increments of one bank of
64 kilobit chips (64 kilobits times 8 chips equals 64 kilobytes per bank). This
allows 320 kilobytes to reside on one memory card if all five banks are installed,
and an additional 320 kilobytes may reside on a second card.
When 256 kilobit RAM ICs become readily available, it will be possible to install
the entire 640 kilobytes on one memory card. The system will accept this configura-
tion only if U455, the memory address decoder, is replaced. This memory address
decoder provides the address logic required by the higher capacity chips. The
replacement U455 device will be made available when it is determined that reliable,
economical, 256K devices are feasible.
The memory configuration is an 8-bit data structure, with odd parity generation
and error detection, to detect even-numbered bit producing errors.
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