Corsair AN806 User Manual

AN806: Memory Upgrade Resource Guide

Mike Clements, Corsair Memory Inc.

Introduction

Here at Corsair we are always looking forward. One current trend we have noticed is the
growing number of people upgrading their desktop PC memory. Due to the progression of
current memory offerings and current motherboard offerings, there are a growing number of
factors to consider before making your upgrade. These factors can greatly impact the
effectiveness of the memory upgrade.

The most critical factors to consider when upgrading the memory in your computer are how
many modules you will have in the system, whether or not you overclock your system, and
which operating system you will be using. These factors are discussed in detail below.

The Number of Memory Modules Used

Most new computers and motherboards have four DIMM sockets. Typically, when a new
computer is purchased, OR when building a new PC, only two of these sockets are
populated. So, upgrading the system is usually done by either [1] adding two more DIMMs
to the pair already in the system, or [2] putting in two new DIMMs and discarding the old
DIMMs.

For users opting to use four memory modules, referred to hereafter as “4-up”, there are
many considerations. First, 4-up places a greater electrical load on the memory controller
than 2-up. This increased load can result in instability if the BIOS is not tuned or tweaked to
compensate. The user should make certain that their motherboard BIOS allows
adjustments to the memory controller voltage. Additionally, users should be certain that
their motherboard is capable of cooling the memory controller as it will generate more heat
with 4-up and the increased voltage.

This increased load of 4-up is not an additional load on the memory modules. Many users
mistakenly increase memory voltage when running 4-up and most often when trying to
address stability issues. This is not necessary as a motherboard is configured to supply the
BIOS set voltage to each slot, regardless of how many slots are filled. Increasing the
memory voltage over the rated voltage should only be necessary when overclocking or
using memory that exceeds the JEDEC specifications for voltage.

A user that already has a pair of modules and adds a second pair should take care to
purchase a kit as similar as possible to the original to have the greatest chance of
successful integration. This ensures a high likelihood of success when running a system
with all four DIMM sockets populated.

The number of modules used can also have an effect on users attempting to utilize EPP or
XMP performance profiles. Some BIOS implementations will not allow the selection of these
options when running 4-up. Operation in the 4-up configuration is not a defined part of the
EPP or XMP standard, and users running 4-up should set their memory settings manually.

Overclocking

If you take a look at a current motherboard with overclocking options, you may see some
specifications similar to this:

 4 X 240-pin DIMM sockets supporting a maximum memory capacity of 8GB
 Supports dual channel DDR2 1066/800/667/533 Un-buffered Non-ECC memory

Many users interpret these specifications too liberally. A motherboard that can overclock to
a given speed with 2 modules cannot overclock to that same given speed with 4-up. Again,
this is due to the increased electrical load on the north bridge or memory controller and the
increased heat that accompanies it. So, many users are disappointed when they add
memory and their overclocking capability is reduced. They tend to fault the memory for this
limitation when it is actually a physical limitation of the memory controller.

A good analogy representing visualization of the above specifications is a passenger truck.
Let‟s assume that the maximum hauling capacity of the truck is 8000 pounds representing
8GB of memory. The top speed of the truck is 106.6 mph representing a memory speed of
DDR1066. However, this does not mean that the truck can haul 8000 pounds at 106.6mph.
The physical limitations are similar for a memory controller as 8GB and 1066 are both
tested maximums for this memory controller. When the memory controller speed is
increased for overclocking, it simply cannot manage the same amount of memory at that
overclocked speed for proper stable communication with the CPU.

Operating System

Currently there are several considerations for memory upgrades that relate to the operating
system. The most common is the use of a 32bit operating system versus a 64 bit operating
system

Memory usage in 32-bit operating systems

Since each binary bit in a 32-bit operating system can be used to represent the location of a
byte of memory, a 32-bit operating system has a maximum „memory address size‟ of 2

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