Computer Memory Buying Guide, RAM, DRAMM, DIMM, FLASH,

Virtual memory is simply your hard drive trying to act like a RAM chip. Since the hard drive is so much slower than real memory, programs stutter and sometimes crash when the hard drive has to do a job it was never designed for. There are only two solutions to this problem: close some programs until virtual memory is no longer needed, or add more physical memory. If you can afford it (and current memory prices are low enough that practically anyone should be able to), the latter solution is always preferable.

To find out how much memory is installed on your PC (if you are running Windows 95, 98, 2000, or NT), right-click My Computer and select Properties from the menu. Make sure the General tab is selected and look for the RAM value at the bottom of the Computer section.

To find out how much memory is installed on your Macintosh computer, select About This Computer from the Apple menu in the Finder. This will show you how much total memory your Mac has, in addition to how much is currently being used by the system.

If your computer uses SIMMs, it will work best with either Fast Page mode or Extended Data Out (EDO) technology. EDO is the faster of the two, but your computer may not support it. These two types of memory also come in several speeds, ranging from 60 nanoseconds at the fast end to 80 nanoseconds at the slow end.

There are two other considerations SIMM users must keep in mind when upgrading. First, look at the contacts in the memory sockets. If they are silver, you'll want a SIMM with tin connectors. If they are gold, get a chip with gold connectors. Doing so will prevent chemical interactions that could eventually short the connections.

The final thing to keep in mind is parity. All you really need to know is if your system is designed to work with parity or nonparity SIMMs. Some work with either, but most only work with nonparity chips. Try to determine to parity of the chips that came with the computer and buy your extra memory with matching specifications.

Most of the PCs sold in the last few years use synchronous dynamic RAM (SDRAM), a technology that helps the memory chip work better with the CPU for better overall performance than even EDO memory can deliver. The most prevalent type of SDRAM at this time is called PC100 SDRAM, where the PC100 means the memory communicates with the computer's central processing unit at 100 MHz (megahertz). Newer computer motherboards use a 133 MHz system bus, meaning the processor and memory can communicate at a faster speed of 133 MHz. For these systems, 133 MHz PC133 SDRAM works best. Just remember PC133 SDRAM is more expensive than the PC100 stuff.

Rambus dynamic RAM (RDRAM) represents the latest technology in consumer-level memory. Developed by Rambus Inc., RDRAM can communicate with the CPU at up to 800 MHz. RDRAM is more expensive than PC133 SDRAM, and your computer's motherboard must specifically support the technology before your can reap its benefits.

Once the case is off and you've discharged your static electricity, pick up the memory chip by its top. Don't touch the silver or gold contacts at the bottom, because even a little oil from your finger can eventually interfere with the connection. Regardless of the type of memory you have, it will only go into the empty memory slot one way, so look at the notches in the contacts and line them up so the partitions in the RAM sockets fit in the grooves.

Here's the tricky part. You want to seat the memory chip firmly in the socket without applying a lot of force, and by applying equal amounts of pressure to both ends of the chip instead of pushing in the middle. This is sometimes tough because of all the wires and cables that obscure many RAM sockets, so do what you can.

The procedure for inserting DIMM chips is pretty straightforward. Make sure the levers on the side of the socket are completely open, and press the new memory chip straight down into the socket. When you meet resistance, stop and try to close the locking levers (they may be closed already). If they close easily, you've probably done it correctly. If not, open the levers fully again, gently pull the chip out of the socket (don't ever rock it back and forth), and keep trying until the chip is seated firmly and the locking levers close fully.

Those of you installing SIMMs will have to use a different approach. These chips are designed to "swing" into place easily. Insert the chip at a slight angle to the RAM socket until you meet resistance, then push both ends of the chip to swing the memory into an upright position in the slot. If all goes well, the clips on both ends will fully snap into place and secure the memory in its new home. If the chip is not positioned fully upright, or if the clips haven't fully engaged, open the clips, gently remove the memory chip, and try it again.

If that still doesn't work, first try taking out the new memory chips and restarting the PC with just its old memory chips in. If everything works OK (it usually will), then turn the machine off again and try removing the old memory and putting the new memory in the slot where the old memory used to be. If the system boots properly in that configuration, there may be something wrong with the memory sockets you were trying to install the new RAM in. If everything does not work when you try rebooting with just the old memory, call your computer manufacturer's tech support.

If the system boots properly on the first try (which it often will), check to see if the system is recognizing all your memory by right-clicking My Computer, clicking Properties, and selecting the General tab. The RAM figure in the bottom of the Computer section should match the total amount of your original RAM combined with the new RAM.

For Mac users: Use the above methods, but select About This Computer from the Apple menu in the Finder. This will show you whether your system has recognized the new memory.