IBM 512KB Memory Expansion Option Manual page 5

Description
The IBM Personal Computer AT 512Kb Memory Expansion
option has 36 RAM modules (128Kb x I) for a total capacity of
",.........., 512Kb.
Memory Cycles
Memory read and write commands require a l-wait-state, 3-clock
memory cycle. Data moves as a byte (8 data bits and 1 parity bit)
or as a word (16 data bits and 2 parity bits) and is parity-checked
on the adapter. A parity error causes an I/O channel check
(non-maskable interrupt) to the system.
Memory Address Switches
There are two banks of memory address switches on each
memory adapter. These switches are set to values for the first,
second, third, etc. memory adapter in the system.
The first memory expansion adapter must start at address space
hex 100000. If more than one adapter is installed, no gaps
between memory are allowed. All expansion memory must be
one contiguous block starting at address hex 100000.
The figure on the following page shows the switch settings for
each adapter.
August 31, 1984
Personal Computer AT 512KB Memory Expansion Option 1