UPGRADING REPAIRING PCs

and higher systems don’t require parity-checked RAM, but will
ignore the parity bit(s) if present.
Parity-checked memory must be used on systems that require it,
and should be used on systems that can be configured to use the
parity bits, especially if the systems support ECC (Error Correction
Code) operation, which uses the parity bit as a means of correcting a
faulty memory bit.
Requirements for ECC Memory Use
ECC requires the following:
• Parity-checked memory modules
• A motherboard chipset that offers ECC support
• ECC support enabled in the BIOS system configuration
ECC operation is recommended for servers and other systems that
are performing mission-critical tasks because ECC operation can
correct single-bit memory errors. Larger memory errors will cause
the system to display an error message and halt.
However, systems using ECC will cost more due to the higher cost
of parity-checked RAM. Additionally, system performance is slightly
slower due to the extra time involved in ECC operation. Check
your motherboard or system documentation to determine whether
ECC is an option for your system.
To determine whether a memory module supports parity-checking
or ECC, use the following tips.
Using the Divide by 3 Rule to Determine Parity Support
Count the chips on a SIMM or DIMM. If you can divide the number
of chips by 3, the module is most likely a parity-checked module.
However, some memory manufacturers have created memory
modules with fake parity chips; these are referred to as logic parity
modules.
Note
Memory Types 43
See Upgrading and Repairing PCs, 12th Edition, Chapter 6, for
more information about how to detect a logic parity module.
Using the Divide by 9 Rule to Determine Parity Support
A similar “divide by 9” rule can also be used to determine parity
checking if you know the number of memory bits in the module.
Note in Table 2.16 that the number of bits in parity-checked