RAM stands for Random Access Memory, what this mean is that when you start up your computer every program that you run goes through this memory some stay in this memory until you turn off the computers power or some are in memory while you are working with windows and a program like "windows write" until you save the memory that's used by your " write text" and exit it than frees up the memory (so basically you put stuff in it and clear it out without actually ever seeing it but the more you have the better today's software will run). The most common type of RAM chips are SIMM's (Single Inline Memory Modules) and DIMM's (direct inline memory modules). Your motherboard will most likely use one of these. There are a couple of different ways to go though. 30 pin or 72 pin or 168 pin SIMM's chips come in 2 sizes: 30 pin is old it is unlikely that you will ever use these again and 72 pin's are actually fading out now, the most common memory now is 168 DIMM memory but some motherboard's can take both 72 pin and 168pin you must also remember that 168 pin DIMM's must also be chosen like the CPU in either 66mhz bus speed or 100mhz..However there is being introduced the PC100 DIMM's, with today's state of the art systems things move at such breakneck speeds that reliability and speed requirements have become an issue and have led to the development of PC100 DIMM's. Designed to cope with the pressing demands of today's and tomorrows software and systems, it provides the major advantages of working with 100mhz motherboard's including BX chipset's and super seven, available without ECC (error correction code), works with 350mhz+ (slot 1), can be fitted singularly and can be use in any combination. Sometimes SIMM's need to be installed in groups. This means that you have the exact same chip in paired slots--they must be the same size and speed. On a 386 or 486 30 pin SIMM's need to be installed in fours, but 72 pin SIMM's don't. Lets say you have a 486 with 2 72 pin slots (slots 1&2) and 4 30 pin slots (slots 3-6). You can put one 72 pin SIMM in slot 1, leave slot 2 empty and fill the rest of the 30 pin slots with SIMM's in a 586 (Pentium) motherboard, 72 pin SIMM's must be installed in pairs. How fast does you memory go... SIMM's are rated in nanoseconds (ns). The faster the better... A 486 probably wants 70-80 ns RAM. A 586 60-70ns. Some 586 motherboard's require 60ns SIMM's. Check the documentation. Its probably a good idea to buy faster RAM so you can use it in other machines down the road. Lower numbers are better. What's Parity or Non-parity? Non-parity. Its cheaper and I think parity SIMM's are only required when some motherboard's require it especially, while the majority of others don't. EDO RAM EDO (enhanced data out) RAM prices have dropped significantly lately so it may be worth it to pay a bit more for it. I haven't used it myself, however. but they say its a lot faster than the standard stuff.
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