IBM PS/2 90 XP 486 Hardware Maintenance Reference page 26

2.4.4 Memory Errors
Type 1 Processor Boards:
only interleaved memory configurations.
(70ns, 80ns, and 85ns) are supported.
Some memory errors will cause a blank display screen.
screen is blank, a POST error code cannot be displayed.
The first 1MB bank of J1 (Model 90) or A1 (Model 95) and the first 1MB
bank of J3 (Model 90) or B1 (Model 95) are the first block.
The second 1MB bank of J1 or A1 and the second 1MB bank of J3 or B1
are the second block.
Any other pairs of memory-module kits, are addressed in the same way;
however, the block size depends on the memory kits installed.
When any defective memory is detected in a bank, the entire block is
disabled.
The following figure shows an example of how memory disabling (after a
memory failure) varies depending on the memory configuration.
+------------------------------------------------------------------------+
¦ Paired Memory ¦ Memory Bank Size ¦ Memory Block
¦ Kits ¦
+-----------------+------------------+-----------------+-----------------¦
¦ ¦
¦ J1 J3 ¦ J1
¦ A1 B1 ¦ A1
¦ 1MB 1MB ¦ 1MB
¦ 2MB 2MB ¦ 1MB
¦ 4MB 4MB ¦ 4MB
¦ 8MB 8MB ¦ 4MB
¦ ¦
+------------------------------------------------------------------------+
Minimum-memory-block size is 2MB for 1MB and 2MB memory-module kits and
8MB for larger memory-module kits.
Note: If a system with only two 1MB kits (one 2MB block) or two 4MB kits
(one 8MB block) installed detects a memory failure, the system
memory diagnostic might not be able to reconfigure the system to
remove the failing memory.
If POST detects an error in the first block of system-board memory, that
block is disabled. If additional system-board memory is installed, the
addresses assigned to the deactivated blocks are reassigned to the next
usable block of system-board memory and a POST error code is displayed.
If an additional block of system-board memory is installed, the
customer-level diagnostic programs (on the default hard disk drive) can be
run to deactivate the defective block and reassign the memory addresses.
The system can then operate with reduced memory capacity.
block will then be ignored by POST during subsequent power-on operations.
If additional system-board memory is not installed, no address
reassignment can occur and the system cannot be used.
Type 2 Processor Boards:
interleaved, noninterleaved, or a combination of both memory
configurations. Only parity memory-module kits (70ns and 80ns) are
supported.
Some memory errors will cause a blank display screen.
screen is blank, a POST error code cannot be displayed.
If the memory is installed in an interleaved configuration, the system
will operate as described under Type 1 Processor Boards; however, memory
errors are handled differently.
memory configuration, the pair of memory module kits containing the error
will automatically be switched to noninterleaved operation to keep the
maximum amount of memory active.
disabled.
The following figure shows how the amount of memory that is disabled
varies depending on the size of the memory-module kit installed.
+------------------------------------------------------------------------+
¦ Memory Module Kit Installed
+------------------------------------+-----------------------------------¦
¦
IBM PS/2 Model 90 XP 486 and 95 XP 486 HMR
Memory Errors
Systems with a type 1 processor board support
Only parity memory-module kits
¦ Disabled
¦
J3 ¦
B1 ¦
1MB ¦ 2MB
1MB ¦ 2MB
4MB ¦ 8MB
4MB ¦ 8MB
¦
Systems with a type 2 processor board support
If an error occurs in an interleaved
Only the failing bank of memory will be
¦ Memory Bank Size Disabled
¦
¦ Copyright IBM Corp. 1990, 1992
2.4.4 - 1
If the display
¦ Memory Now ¦
¦ Usable ¦
¦ ¦
¦ ¦
¦ ¦
¦ 0MB ¦
¦ 2MB ¦
¦ 0MB ¦
¦ 8MB ¦
¦ ¦
The defective
If the display
¦
¦