8/7/2019 The ddr

http://slidepdf.com/reader/full/the-ddr 1/3

The most important properties are:

• Memory size (in megabytes or gigabytes).

• Memory format (typically DIMM or SO-DIMM).

• Memory technology (for example DDR or DDR2).

•

Memory speed (for example PC2700 or PC133).

Memory Size

The memory size (or capacity) is usually easiest to identify. Modules are available indifferent sizes, for example 256 MB, 512 MB or 1 GB (= 1024 MB). In general more

means better. The more memory you have installed in your system, the easier it will cope

with heavy tasks and running simultaneous tasks will be more smoothly. There is amaximum amount of memory. The maximum is determined by the amount of memory

 banks on the motherboard and the chipset which is also mounted on the motherboard.

Memory Form Factor

This concerns the physical dimensions of the memory modules. It is closely related to the

memory technology which is discussed in the next paragraph. In general one candistinguish two memory form factors: DIMM (Dual Inline Memory Module) and SO-

DIMM (Small Outline DIMM). This roughly translates to the difference between

desktops and notebooks. There are exceptions to this rule so always check the technicaldocumentation of your system.

Memory Technologies

As technology evolves, changes are made to the way the memory is placed and used in a

system. This means that the sockets for memory have changed, and/or the voltage inthose sockets has changed and so on. Due to these changes, there are differences in the

"packaging" of memory modules. The most important are:

SDRAM or SDR (Synchronous Dynamic Random Access Memory):

This memory is available in two types: DIMM and SO-DIMM and operates at 3.3 V. The

SDRAM DIMMs have 168 pins and two notches (to ensure proper placement of the

module). The SDRAM SO-DIMMs have 144 pins and one notch.

SDRAM DIMM SDRAM SO-DIMM

DDR (Double Data Rate) SDRAM:

This type of memory is also available in two types: DIMM and SO-DIMM. To avoid

confusion they are referred to as DDR DIMM and DDR SO-DIMM. This memory

8/7/2019 The ddr

http://slidepdf.com/reader/full/the-ddr 2/3

operates at 2.5 V. DDR DIMMs have 184 pins and one notch. DDR SO-DIMMs have

200 pins and one notch.

DDR DIMM DDR SO-DIMM

DDR2 SDRAM:

Also this type of memory is available in DIMM and SO-DIMM formats. DDR2 is an

evolution of DDR and enables higher speeds and lower power consumption. The DDR2DIMMs have 240 pins and one notch, the SO-DIMMs have 200 pins and one notch. The

notch on DDR2 SO-DIMMs is placed slightly different than with DDR SO-DIMMs to

 prevent using the wrong type of memory.

DDR2 DIMM DDR2 SO-DIMM

Memory Speed

The memory speed indicates how fast the memory can exchange data with the rest of thesystem. This speed is often indicated in Megahertz (MHz). One Hertz means one

operation per second. Normal SDRAM allows one operation at a time, while DDR can

 process two operations in the same time (hence the term double data rate). In other speedindications, this speed is translated in to the amount of data, in megabytes, the memory

can transfer per second. Unfortunately the two notations are used both and causes

confusion. The types of memory that are available at this moment are the following:

SDRAM:

• PC100: SDRAM, operates at a maximum of 100 MHz.

• PC133: SDRAM, operates at a maximum of 133 MHz.

DDR SDRAM:

• PC2100 or DDR266: operates at a maximum of 133 MHz.

• PC2700 or DDR333: operates at a maximum of 166 MHz.

• PC3200 or DDR400: operates at a maximum of 200 MHz.

DDR2 SDRAM:

• PC2-4200 or DDR2-533: operates at a maximum of 266 MHz.

• PC2-5300 or DDR2-667: operates at a maximum of 333 MHz.

Selecting the Right Speed

8/7/2019 The ddr

http://slidepdf.com/reader/full/the-ddr 3/3

The optimal speed of a memory module is closely related to the type of chipset and CPU

used. When upgrading the memory choose memory rated at the same speed or faster than

the one you have currently installed. In technical documentation, you will find thememory speed that a motherboard can support. If, for instance, the specifications state

that your motherboard supports PC2100 and PC2700 memory, it is not said that PC3200

will not work. As a matter of fact in the vast majority of cases it will work properly. Itmay run at a lower speed though.

Dual Channel

On selected chipsets you have the performance enhancement of Dual Channel memory.

When a system operates in Dual Channel mode, two memory modules are seen as one.

This enables the system to send twice as much data at a time to the modules and retrievetwice as much.

For systems that can operate in Dual Channel mode, two identical memory modules are

needed. Place the modules in the identically coloured memory banks.

Other Technical Terms

In some advertisements you might find other technical characteristics, like CAS latency,or series of digits (e.g. 2-2-4-5), or other speed indicators as given above. Most of the

time this information is given for the enthusiasts that want to squeeze the last bit of 

 performance from their equipment. However, differences are usually not that big whilethe memory is more expensive, and it requires a lot of time and patience to get the best

from this. For normal use, where stability and reliability are more important, these

 parameters play no serious role.

Finding Memory Information

Firstly we need to determine the amount of memory currently installed and how much

memory the computer can support. If we know this we need to know if there are free

memory slots (banks) available. The easiest way to obtain this information is to check thetechnical documentation shipped with your system (i.e. InfoCentre) or the Packard Bell

web site. These sources will contain will contain the information you need to upgrade the

memory of your computer.