Hardware Reference
In-Depth Information
Caution
If your system supports dual- or tri-channel memory, be sure you use the correct memory
socketstoenablemultichanneloperation.Checkthedocumentationtoensurethatyouusethe
correct sockets. Most multichannel systems still run in single-channel mode if the memory
is not installed in a way that permits full multichannel operation, but performance is lower
thanifthememorywereinstalledproperly.Somesystemsprovidedual-channelsupportifan
odd number of modules is installed, as long as the total capacity of two modules installed in
one channel equals the size of the single module in the other channel and all modules are the
same speed and latency. Again, check your documentation for details.
Memory Module Speed
When you replace a failed memory module or install a new module as an upgrade, you
typicallymustinstallamoduleofthesametypeandspeedastheothersinthesystem.You
can substitute a module with a different (faster) speed, but only if the replacement mod-
ule's speed is equal to or faster than that of the other modules in the system.
Some people have had problems when “mixing” modules of different speeds. With the
variety of motherboards, chipsets, and memory types, few ironclad rules exist. When in
doubt as to which speed module to install in your system, consult the motherboard docu-
mentation for more information.
Substitutingfastermemoryofthesametypedoesn'tresultinimprovedperformanceifthe
system still operates the memory at the same speed. Systems that use DIMMs or RIMMs
can read the speed and timing features of the module from a special SPD ROM installed
on the module and then set chipset (memory controller) timing accordingly. In these sys-
tems, you might see an increase in performance by installing faster modules, to the limit
of what the chipset supports.
To place more emphasis on timing and reliability, there are Intel and JEDEC standards
governing memory types that require certain levels of performance. These standards cer-
tify that memory modules perform within Intel's timing and performance guidelines.
The same common symptoms result when the system memory has failed or is simply not
fast enough for the system's timing. The usual symptoms are frequent parity check errors
or a system that does not operate. The POST might report errors, too. If you're unsure of
which chips to buy for your system, contact the system manufacturer or a reputable chip
supplier.
See
“
Parity Checking
,
”
p.
347
(this chapter).
