Introduction
Computer memory comes in a number of different forms, speeds, sizes and types. EDO, SDRAM, SIMMs, DIMMs… So how are you supposed to know what you need?
Figuring Out What You Need
The very best way to figure out what you need is to consult your computer’s manual. If you do not have a manual, check our links page for your computer manufacturer’s website. You can typically track down the information you need if you know what model computer you have. If you are still having trouble, call us.
Memory Terminology
RAM
Random Access Memory, which is the technical name for the memory you can add to your machine.
ROM
Read Only Memory, which comes built into your motherboard and cannot be increased.
Bus Speed
The speed at which your motherboard operates, measured in megahertz (MHz). The memory you buy must be compatible with your motherboard speed. If your motherboard operates at 100MHz, then you need PC-100 memory.
Memory Speed
The speed at which your memory operates, measured in nanoseconds (ns). The faster the memory speed, the more efficiently your computer will run.
Memory Voltage
Typically either 3.3 volts or 5 volts. PCs typically use 3.3v memory, while Macintoshes use 5 volt memory.
EDO
Extended Data Out RAM, also called Hyper Page Mode RAM.
SDRAM
Synchronous Dynamic RAM. Faster than EDO RAM.
ECC
Error correcting memory. It has the ability to check written data for some types of errors and discard it if errors are found without interrupting processing. It is usually only used in mission-critical computers like network servers, where memory errors and the subsequent crashes they generate cannot be tolerated.
Parity
A method of memory error checking in which an extra bit of data is written by the memory and sent to the device receiving the data, which then uses the extra bit (the parity bit) to check whether the received data is valid.
SIMM
Single Inline Memory Module. They come in 30 pin (basically obsolete) and 72 pin versions. SIMMs often have to be installed in pairs. EDO is the most common SIMM memory type.
DIMM
Dual Inline Memory Module. DIMMs have 168 pins and are installed one at a time. SDRAM is the most common DIMM type.