UPGRADING REPAIRING PCs

46
Chapter 2—System Components and Configuration
Restart system and
enter BIOS setup under
advanced or chipset
setup, select memory
timing parameters and
set all to BIOS defaults.
Save settings and reboot.
Retest as shown in
Figure 6.17.
Problem
not solved
Open your system case.
Identify the SIMMS/
DIMMS/RIMMS.
Determine the bank
arrangement. Remove
and reinstall all of the
memory modules to
reseat them. Ensure that
they are the correct size,
speed, voltage, and type
for your system.
If problem remains with
all but 1st bank removed,
problem isolated to 1st
bank. Replace memory
modules.
Problem solved
Problem solved
If problem does not
recur after removing/
replacing modules, could
be that contacts need
cleaned.
Problem
not solved
Problem solved
Figure 2.12 Testing and troubleshooting memory.
Memory Usage Within the System
Note which are the
slowest.
If problem was solved,
the improper BIOS
settings were the culprit.
If problem is solved with
all but bank 1 removed,
the problem could be in
one of the modules you
removed. Add 1 at a time,
and retest. When problem
appears, replace module.
If problem still remains
after all banks are tested,
replace motherboard.
The original PC had a total of 1MB of addressable memory, and the
top 384KB of that was reserved for use by the system. Placing this
reserved space at the top (between 640KB and 1,024KB instead of at
the bottom, between 0KB and 640KB) led to what is often called the
conventional memory barrier. Systems with more than 1MB of RAM
treat the additional RAM as extended memory, beginning at 1MB.
Thus, there is a “hole” in memory usage between 640KB and 1MB.
Some standard add-on cards and motherboard devices use part of
this memory area for RAM and ROM addresses, leaving the remainder
of this space free for additional card usage.
Hardware and Firmware Devices That Use Memory
Addresses
The listing of hardware and firmware devices that use memory
addresses is relatively short when compared to IRQ, DMA, and I/O
port address usage, but it is no less important. No two devices can
share a memory address. Table 2.18 shows memory usage in the
640KB–1MB memory range for standard devices.