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Recognize the Different Kinds of Memory

RAM comes in many different kinds of configurations and types—and runs at many different speeds, as well. before you upgrade, you need to know how to spot the different types. Pictured here are the different types of RAM, including the older-style DIPs and newer SIMMs, DIMMs, SDRAM, and Rambus memory (often called RIMMs).

Dual Inline Packages (DIPs)

If you have an older computer, it might use an older kind of memory called a dual inline package (DIP). DIPs plug directly into their own sockets on the motherboard. It's difficult to find DIPs today because they're old. They come in pairs or sets of eight.

Figure 3.2

Single Inline Memory Modules

SIMMs (single inline memory modules) plug into long, matching sockets on your motherboard. SIMMs have more capacity than DIPs. Typically, a motherboard has several banks of SIMM sockets into which you plug SIMMs. SIMMs come in 30-pin and 72-pin formats. 30-pin SIMMs usually have less capacity than 72-pin, and often come with capacities of 256k, 1MB, 2MB, and 4MB. 72-pin SIMMs come in 1MB, 2MB, 4MB, 8MB, 16MB, and 32MB.

Figure 3.3

DIMMs, SDRAM, and Rambus

DIMMs (Dual Inline Memory Modules) look much like SIMMs, but they come in a 168-pin format. They are usually a faster and higher-performance memory than SIMMs, and are used in Pentium PCs. They come in capacities ranging from up to 64MB and beyond. Newer kinds of memory, synchronous DRAM (SDRAM), and Rambus memory (often called RIMMs), run even faster, and also come in capacities up to 64MB and beyond.

Figure 3.4

ECC Versus Non-ECC

A SIMM or DIMM usually has nine chips of memory on it. Eight of those chips are used for the memory itself. The ninth chip is called a parity chip. The parity chip is used for error checking, to make sure that the other chips aren't making any errors. some computer systems require parity chips, whereas others do not. In newer kinds of memory, such as SDRAM and Rambus, you don't refer to parity or nonparity—instead you refer to error correcting code memory (ECC) or non-ECC. Check your PC or motherboard's manual to see which kind of memory your PC requires.

Figure 3.5

Memory Comes in Different Speeds

The faster the memory, the faster a computer operates. memory comes rated at different speeds, and the faster the memory, the more it costs. Memory speed is measured in nanoseconds, and the lower the nanosecond rating, the faster the memory. For example, a 60-nanosecond chip is faster than an 80-nanosecond chip. Be sure that the memory you buy is as fast as the memory you're replacing. Many newer, faster Pentiums come with SDRAM and Rambus memory RAM that run much faster. Rambus memory can run at 600Mhz, 700Mhz, and 800Mhz, whereas SDRAM runs at 100Mhz or 133Mhz—the speed of the system bus.

Watch Out!

You can use memory with parity chips on a computer that doesn't require parity chips. Memory without parity chips, however, won't work on a computer that requires parity chips.

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