RAM explained
Think SIMM and DIMM are characters from a Dr. Seuss book? Don't be intimidated by acronyms. We'll help you figure out what separates your RAM from your DRAM.
Your computer uses at least two types of memory: long term and temporary (you may also find memory chips on components such as video adapters, but we'll save that discussion for another day). Long term memory is found in hard drives and other storage devices; temporary memory is memory that is used only when the computer is on and functioning. Once you turn off your computer, the temporary memory vanishes. Temporary memory in your computer is referred to as RAM.
What is RAM?
Every time you start your operating system, launch a program, or open a file, all the data involved is loaded into RAM. That's why you see RAM listed in the system requirements for the software you buy. If you have more RAM, you can open more files or programs at once, and load bigger files or programs onto your system.
RAM is rated in terms of megabytes (MB), and a typical computer will ship with 64MB to 128MB installed. However, you can increase that total to 256MB, 512MB, or even a whopping 1GB, if your system supports it.
What are the different types of RAM?
Memory comes in a variety of packages, pin configurations, types, and formats. Are you looking for SIMMs, DIMMS, or RIMMs? How many pins should they have? Do you need parity or ECC? FPM or EDO? Confused yet? If "PC100 Sdram NonEcc" makes your eyes glaze over, you've come to the right place.
There are two basic types of RAM available today: SDRAM (Synchronous Dynamic RAM) and RDRAM (Rambus Dynamic RAM). And, there are three incompatible forms of SDRAM memory modules currently in widespread use. The form you need depends on the RAM sockets installed on your motherboard. Most systems available on the market today take SDRAM in 168-pin DIMMs (dual in-line memory modules); older Pentiums and later 486 PCs take 72-pin SIMMs (single in-line memory modules), while earlier 486 desktops take 30-pin SIMMs.
RAM modules are usually a little over an inch wide and four to six inches long--look for a row of slots projecting from the motherboard with at least one module plugged in. The number of pins refers to how many gold (or tin) contact strips are on the edge connector side of the SIMM or DIMM.
You can buy DIMMs that hold up to 256MB or more, but note that not all motherboards support all module sizes. To get an idea of the limitations of your system, check your motherboard or PC manual. 30-pin SIMMs are rarely produced anymore and expensive. If you're thinking of getting 30-pin SIMMs to speed up an older machine, shop around first because in the long run, it may just be cheaper to purchase a whole new system.
By Samuel Brown Baker II, Margaret Chesler, Robert Vamosi, Special to ZDNet
