Table of Contents
Advertisement
Error Recovery
lf POST detects a memory error in any part of the system-board
memory, an attempt is made to deactivate the physical 1MB block of
memory that contains the error.
The addresses assigned to the
deactivated block are reassigned to the next physical block of
system-board memory, if installed (the first 1MB of memory-address
space cannot be assigned to memory installed in any of the micro
channel connectors).
If 1MB of valid system-board memory cannot be
found, the system sets the memory size according to the last good
memory available and allows a system reset; however, if a minimum
of 64KB of good memory cannot be found, POST cannot recover from
the error.
If the first physical 1MB of memory is disabled, the split-memory
block and ROM-to-RAM
remap feature will not be enabled.
System-Memory Map
Memory is mapped by System-Board POS Register 5 (hex 0105).
Warning:
IBM recommends that programmable options be set only
through the System-Configuration utilities.
Directly setting the POS
registers or CMOS RAM POS parameters can result in multiple
assignments of the same system resource, improper operation of the
feature, loss of data, or damage to the hardware.
The first 640KB of system-board RAM is mapped starting at address
hex 000000.
A 256-byte and 1KB portion of this RAM is reserved as
BIOS data areas.
See the /BM Personal System/2 and Personal
Computer BIOS Interface Technical Reference manual for details.
Figure
3-5 on page
3-10 shows the memory map for a properly
functioning system.
Memory can be mapped differently if POST
detects an error in system-board memory or RT/CMOS RAM.
In the
following figure, the variable X represents the number of 1MB blocks
of system-board memory starting at or above the hex 100000
boundary.
The variable Y represents the number of 1MB blocks of
addressable memory installed in the channel starting at or above the
hex 100000 boundary (Y cannot exceed 14.75).
Model 65 System Board
— October 1990
3-9
Advertisement
Table of Contents
