Table of Contents

• Step 1: An Introduction to Memory
• Step 2: Buying your RAM
• Step 3: Installation

Step 1: An Introduction to Memory

System memory is stored in physical memory banks referred to as RAM. RAM comes in "sticks" that connect to your motherboard. A stick of desktop RAM is called a DIMM, while its laptop counterpart is called a SODIMM. The RAM you want to buy will look like this:

NOTE: Most people use the terms "system memory" and "RAM" interoperably. Unless you're a computer science major, there isn't really a difference.

Just as animals are distinguished by their genus and species, system memory is usually identified by two factors: its family and its front side bus (FSB). Before you can buy more memory, you will first need to know what kind to buy or it may not work with your computer.

Family matters

There are currently 3 main families of RAM on the market at the moment. They are:

• SDRAM - While all three of these families are technically members of the Synchronous Dynamic RAM family, the term SDRAM is usually used to refer to an a previous (older) generation of RAM technology. If your computer was made in 2001 or previous years, you probably have a form of SDRAM running in your system.

• DDR - The past few years have seen "Double Data Rate" or DDR SDRAM replace ageing SDRAM--mainly due to the fact that it promises roughly twice the performance. DDR is slowly being replaced by DDR2 (see below). Unless you bought your computer within the last year, your machine probably has DDR.

• DDR2 - A new form of DDR that has been embraced by Intel, but has yet to see significant performance benefits over its predecessor. Computers with the latest generation of Intel processors (especially those using the LGA775 socket type) probably have DDR2 RAM.

A computer will only support one family of RAM, so make sure you buy the right kind.

Not the Magic School kind

Inside a family, sticks of RAM can differ by their front side bus, a measure of how fast the RAM can "talk" to your processor (CPU). FSB is measured in megahertz (MHz)--the larger the number the "faster" the RAM. FSB ranges within a particular family are as follows:

• SDRAM - 133MHz (slower speeds are no longer sold)
• DDR - 266MHz, 333MHz, 400MHz
• DDR2 - 400MHz, 533Mhz, 667MHz, 675MHz

Note: DDR400 really has a FSB of 200MHz, not 400Mhz. However, "double" in DDR's name means that it can transfer twice as much data per clock tick (1 Hz), thus the effective FSB is 400 MHz. However, some e-tailers like to be brutally honest when listing DDR stats, so don't be confused if you see 200Mhz DDR.

Luckily, a computer will support all FSB ranges in a particular family. However, all DIMMs must run at the same FSB, even if some are faster than others. This means that if you buy a slow stick of RAM, the rest of your RAM will slow down.

Nomenclature...of DOOM

A typical listing of memory for sale will look something like this:

• Corsair ValueSelect DDR400 (PC3200) - 1GB (2 x 512MB)

Oh dear...those silly engineers have been hard at work I see. This actually makes sense if we break it down into parts.

• Corsair - the name of the company that makes the RAM
• ValueSelect - the brand name
• DDR400 - the family (DDR) and the FSB (400 MHz)
• PC3200 - the bandwidth, which, in true engineering fashion, is really just another way of saying the same thing as above, since the FSB and bandwidth are directly related: thus, all DDR400 RAM will have a bandwidth of 3200 MB/s (PC3200).
• 1GB (2 x 512MB) - a previously unmentioned value, the capacity of the module for sale. RAM sticks come in 128MB, 256MB, 512MB, and 1024MB (1 GB) flavors. Remember that we want to end up with at least 512MB of RAM in your system, so make sure that the amount that you're buying + the amount you already have will equal that amount. Also note the fact that this is really two sticks of 512MB each, not one stick of 1GB.

Okay, enough with the learning! It's time to go buy some RAM. Head on to Step 2 for more information.