Don't mix up PC memory, disk storage

Not long ago I recommended that folks who want to upgrade to Microsoft Windows XP increase their computer's memory to 256 megabytes. This, in turn generated the usual confusion from people who told me they already had 10 gigabytes of memory and thought that was certainly plenty.

So I guess it's time to talk about memory - what it is and why your computer probably needs more. First, let's eliminate the confusion about memory vs. hard disk storage. Random Access Memory, known as RAM, consists of chips that store the programs and data your computer is actually using when it's running. When you turn off your computer, the contents of RAM disappear.


A lot of folks mistake RAM for hard disk storage, which is another kind of memory. Your hard disk stores programs and data permanently, even when you turn off your computer.

When you start your PC, its first job is to transfer the operating system from the hard drive to RAM, along with any programs you subsequently run and any documents you call up. When you write a letter to Aunt Rhoda, it's stored temporarily in RAM while you create it, and then permanently on your hard drive when you save the document. If you want to change what's in the missive the next day, your word processor summons it from the hard drive into RAM and puts the revised letter back on the hard drive when you're through.


RAM is generally measured in megabytes, or millions of bytes (abbreviated MB). Computers typically come with 128 or 256 MB of internal memory today, although machines sold only a few years ago often had only 32 or 64 MB.

Hard disk storage is measured in gigabytes, or billions of bytes (abbreviated GB). Most of today's machines come with 20 to 40 GB hard drives - three to four times as much as computers built a few years ago.

Why is memory so important? Because Windows and application programs such as word processors, e-mail clients, spreadsheets, Web browsers, photo editors and digital music players use lots of it.

Windows itself consists of many different programs that operate simultaneously. To see for yourself, start up your computer, and when Windows is finished loading, hold down the CTRL, ALT and DEL keys simultaneously. A box will appear showing the major programs running at the moment. You might not recognize most of them because they're part of Windows' internal workings. Hit CANCEL to make the window disappear.

This view only scratches the surface, by the way. If you delve into the System Information program from the System Tools section of your Accessories menu, you might find 200 or more different snippets of code running at the same time.

Each program requires its own memory space. When programs get too crowded, they may invade each other's space and crash, like dancers on a crowded nightclub floor. Or they may step on Windows' code space and cause your computer to crash completely. One of Windows XP's main advantages is better memory management - total crashes are relatively rare.

When Windows uses up all available RAM, it starts shuffling data back and forth from your hard disk, using the drive as something called Virtual Memory. This keeps your computer running but slows it down by orders of magnitude. If you're into kitchen metaphors, the difference in speed between fetching data from memory and searching for it on a disk drive is the difference between grabbing a can of tuna from the cupboard and running down to the corner store to buy it.

With enough memory, your system won't have to run to the store as often - which means it will operate faster and more reliably.


How much memory do you need? If you're running Windows 98 or ME, 128 MB is enough for most applications, although 256 MB will smooth operations considerably. On older computers, you might find a startling improvement in speed by upgrading from 64 to 128 MB. Windows XP will run in 128 MB of memory, but I wouldn't try it with less than 256 megs. It's a real hog.

Going beyond 256 MB won't necessarily improve performance unless you're involved in memory-intensive applications such as high-resolution digital photography or video production.

Luckily, memory is dirt cheap these days. I shopped online and found the most common 128 MB modules available from reputable companies for $18 to $40. Most Pentium 4 machines require a different kind of high-speed memory that costs about twice as much, but either way, upgrading your machine to 256 MB won't break the bank.

You'll usually pay another premium if you have a laptop computer. Most portables require proprietary memory chips designed by the manufacturer. These are far more expensive than standard RAM modules that fit desktop machines.

The easiest way to upgrade memory is to take your PC to a computer retailer or repair shop. Many will install the chips you buy on the spot, either free or for a nominal charge. This is more expensive than buying RAM online and doing the job yourself, but you don't have to worry about what kind of chips to order or muck around inside your computer. My recommendation: Unless you like tinkering, pay the man.

If you don't mind getting your hands dirty, adding RAM is the easiest computer upgrade. The chips are mounted on small, rectangular circuit boards known as Dual Inline Memory Modules, or DIMMs. These fit into slots on the main circuit board (or motherboard) of your computer. Over the years, memory chip design has changed, so you need to know what kind of chips your motherboard requires. To figure this out, you'll have to wade through the Acronym Swamp - so lace up your boots and read on.


The most common type of memory is known as SDRAM (Synchronous Data Random Access Memory). Most Pentium II and Pentium III machines use it. Newer computers may use something called DDR (Double Data Rate) RAM, which is somewhat faster and more expensive. The original Pentium 4 chipset from Intel required yet another kind of memory chip using technology licensed from Rambus Technologies. It's known as RDRAM or RIMM. It was supposed to be really fast, but mainly it was really expensive. So some manufacturers are now turning out cheaper Pentium 4 systems that use SDRAM with only a marginal loss in performance.

If you have a machine that's more than three years old, it might use older memory modules that I haven't listed. Some older machines also are picky about what size memory modules you can mix and match. That's why it's a good idea to consult the manual that came with your PC and do some research before you buy.

Two good sources of information are Kingston Technology ( and Crucial Technology ( They're online memory retailers whose sites have search systems that will help you figure out what kind of memory you need.