PC Hardware A Beginner’s Guide

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Chapter 7: Computer Memory^139


The earliest type of memory module was the single inline memory module (SIMM). A
SIMM consists of DRAM chips soldered to a small circuit board with either a 30- or 72-pin
connector. A SIMM has a storage capacity that ranges from 1MB to 128MB. At the upper
end of this range, SIMMs have DRAM chips mounted on two sides of the circuit board.
Matching a SIMM to a motherboard and its memory slots involves only matching the num-
berofpinsinthemountingslottothatofthememorymodule.AsillustratedinFigure7-5,a
SIMM is installed on a motherboard in a way that increases the number of modules and the
amount of memory in a relatively smaller area than was required by DIP memories.


Dual Inline Memory Modules


Newer PCs, especially those with 64-bit systems, use an adaptation of the SIMM, the dual
inline memory module (DIMM). This 168-pin module includes DRAM memory on both
sides of the module and supports larger amounts of memory capacity. Matching a DIMM
(see Figure 7-6) to a PC is more complicated than just matching the number of pins.
DIMM modules are available in different voltages (3.3v and 5.0v) and are either buffered
or unbuffered to match up with motherboards and chipset combinations.
A smaller DIMM version is the small outline DIMM (SODIMM), which is used primarily
in portable computers.


Figure 7-5. A SIMM memory module on a motherboard
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