Most memory sold now-a-days does not have even error detection logic, much less error correction (ECC). When you get an error, the program continues, but with wrong information. This may not be all that important if you are just playing a game, but it could be crucial if you are doing an income tax return. Parity memory is a very simple form of error detection without correction. Because of alpha particle emissions, memory can be expected to make errors every so often, even when it is functioning perfectly.

To upgrade RAM, you must check the motherboard manual too see what kinds and combinations of memory it can take. If you have no manual, try the website of the motherboard or computer manufacturer. You could even ask the vendor who sold you the computer, but that information is usually not trustworthy. you can also try the Azen memory configurator. Before you shop you need to know if the memory is:

• 72-pin SIMM, or 144-pin SODIMM or 168 or 184-pin DIMM.
• Capacity per module: 64 MB, 128 MB, 256 MB, 512 MB, 1024 MB/1 gig.
• speed: PC-66, PC-100, PC-133, PC-800, PC-1600/DDR200, PC-2100/DDR266, PC-2700/DDR333, PC-3200/DDR400, DDR2-667MHz.
• type: fast page mode, EDO, SDRAM, ESDRAM, SLDRAM, DDR, RAMBUS/RDRAM, DDR2, hypertransport.
• voltage: 5 volts, 3 volts.
• buffered or unbuffered.
• plain or ECC (error correcting).
• Other modifiers such as CL2, CL3 and registered.

Most new machines use DDR RAM, value machines SDRAM and premium machines RDRAM.

New machines tend to come configured with too little RAM for that class of machine in order to shave the advertised price. Nearly always you should buy the offered RAM upgrade to double the available RAM. You should be thinking 512 MB or 1 Gig to start. The other advantage of buying up front in the RAM type may not always be easily available.