The Basics

Computer memory is the unsung hero of a PC's performance. If you have too little, it can create a huge bottleneck that slows down everything from opening applications to Web browsing. Many experts say that you can never have too much, and while there is a point of diminishing return, adding computer memory is one of the least expensive ways to boost your system's performance. We'll talk about what computer memory is, the various types available, and what to look for when you're shopping for more for your system.

Computer memory is known as RAM (Random Access Memory). It's a form of short-term data storage for PCs, as opposed to hard drives and flash memory drives that allow for long-term storage of data. You can't save any data to your computer's memory--when you reboot your system, all the information currently flowing through the memory is lost. For example, if you have a term paper you've been writing, you can load an old version from the hard drive into your computer's memory by opening it with a word processing program. Then you can manipulate it and make changes. But you'll want to save it often, because you're just holding it in the RAM, and if your computer crashes you'll lose the current unsaved version.

This is an oversimplified way of looking at computer memory; There are lots of ways that modern computers can use hard drive space to expand their working memory, but it shows the importance of having enough RAM. If you're limited to, say, 256MB of RAM and running Windows XP or Vista, you take up most if not all of that just running the operating system, so opening programs or Web sites will take a lot longer.

Like any storage device, RAM is measured in megabytes and then gigabytes (1 gigabyte equals roughly 1000 megabytes). Most new computers ship with at least 512 megabytes (MB) of RAM if not a full gigabyte (GB). We'll talk more about how much RAM you want with your system depending on what you use your computer for.

But not all RAM is created equal. Computer memory has varying speeds that measure how fast that information can be loaded into it or out of it. Like a CPU, memory speed is measured in hertz (cycles per second). For example, if you have memory that operates at 400MHz, that means that it can handle 400 million cycles per second.

Newer computer memory is all DDR--double-data rate memory. By processing data on the upswing as well as the downswing, DDR memory essentially doubles the performance speed. Most systems ship with DDR2 memory, the second generation of double-data rate memory, and a lot of video cards use even faster DDR3 memory.

RAM fits into your computer's motherboard as DIMMs (dual inline memory modules) that pop into slots on the motherboard, usually next to the processor. DIMMs also vary in size, so only certain types of memory can fit into certain types of motherboards. We'll talk more about making sure you get the right computer memory for your system in our five questions:

1) What kind of memory does my computer need? Not all memory works with all computers. In fact, you need to make sure that the memory you're thinking about buying will work with your computer. Most memory manufacturers such as Kingston (www.kingston.com) and Crucial (www.crucial.com) have search engines that will show you what type of DIMMs will work with your computer or motherboard manufacturer. Remember, you don't have to buy directly from these companies--you can just use their memory configurator to find out what RAM works for your system.

2) How much memory should I have? The short answer is, it depends. In general, the more the better. You don't want any less than 512MB to run Windows XP and 1GB is even better (especially if you're thinking about upgrading to Vista). Most users are fine with 1GB, although if you do any graphics or video editing, you'll want to think about upgrading to 2GB or more.

3) What's a good price for memory? Computer memory used to be very expensive, but as with most technology, the prices have dropped considerably over the years. Prices vary quite a bit from manufacturer to manufacturer as well as with the type of memory, but $50 to $75 per gigabyte of DDR2 RAM is a very fair price to pay.

4) How fast of computer memory should I get? In general, the fastest your computer will support. If you have a newer computer, getting 533MHz or 667MHz DDR2 will provide a significant boost over 400MHz memory. But again, you have to make sure that your computer will handle that faster memory. And if you mix memory--for example, having 512MB of 333MHz memory and 512MB of 400MHz memory in two different DIMM slots--the memory will only operate at the slower speed.

5) How do I install computer memory? Installing computer memory is one of easier PC upgrades to make, but it still involves getting inside your system. Power your PC down, unplug the power cord, and then remove the case cover. The DIMM slots are usually located next to the processor. Make sure you have the notch in the DIMM lined up with the slot correctly and push one side in and then the other. The DIMM should click into place and the side ejector tabs will snap in securely.

How to Shop

Computer memory can vary quite widely in price from vendor to vendor--even DIMMs of the same speed from the same manufacturer--so it's best to shop around. Start out by using a memory configurator at a manufacturer Web site such as Kingston.com or Crucial.com. Write down the type of memory that your system can support and then you can start searching for the best price.

In our experience, buying memory online is much less expensive than going to your local brick-and-mortar store. About the only reason to buy at a local retailer is if you're not comfortable installing the memory yourself. Most local retailers will install the memory for a nominal fee--sometimes for free.

A broad Web site that covers a wide variety of vendors such as Shopping.com will often yield the best price for computer memory. Just be sure that the vendor you chose is a trusted one--it may be worth the extra couple of dollars to go with a company you've shopped with in the past. And watch shipping charges: Memory is small and light, so you shouldn't have to pay much (if anything) for shipping. Also check the manufacturer's Web site for any rebates they might be offering--computer memory is one of the product categories that almost always has some sort of rebate offer available.