PC Hardware in a Nutshell, 3rd Edition

Upgrading Newer Systems

Newer systems use DIMM or RIMM modules exclusively. DIMM and RIMM memory are available in many more variants than SIMM memory, so be careful to buy DIMMs or RIMMs that match your requirements. Use these guidelines when choosing DIMM or RIMM memory modules:

• For SDRAM DIMMs, get the proper voltage. All DDR-SDRAM DIMMs use 2.5V. Most SDR-SDRAM DIMMs use 3.3V. Some DIMMs, often called Macintosh DIMMs, use 5V. Some early DIMM-based PC motherboards use 5V DIMMs.

• DIMMs are available in EDO, SDR-SDRAM, and DDR-SDRAM. Some transition motherboards support two types—EDO and SDR-SDRAM, or SDR-SDRAM and DDR-SDRAM. If you have the choice of EDO or SDR-SDRAM, buy SDR-SDRAM DIMMs for future flexibility. If your motherboard supports both SDR-SDRAM and DDR-SDRAM, buy DDR-SDRAM.

• SDR-SDRAM and DDR-SDRAM DIMMs are available in buffered (also called registered) and unbuffered versions. Some motherboards accept only buffered DIMMs, others accept only unbuffered DIMMs, and still others will accept either buffered or unbuffered DIMMs, but do not allow mixing types. Check the motherboard or system maker’s documentation or web site to verify which type(s) of module your system accepts. If you are upgrading an existing system that accepts both types, open the lid to determine which type is currently installed. Even if the motherboard accepts mixed buffered and unbuffered DIMMs, avoid mixing types if possible.

• Buy the fastest-speed memory available, which usually costs little or no more ...