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Table Of Contents  CertiGuide to A+ (Core Hardware)
 9  Chapter 0011:  System Memory
      9  IV  RAM Packaging

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Dual Inline Package (DIP)
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Dual Inline Memory Module (DIMM)
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Single Inline Memory Module (SIMM)

The first implementation of this new packaging was called a Single In-line Memory Module, or SIMM. These packages had a series of DIP chips soldered into a small circuit board with a row of tin or gold contact points on one edge. The first SIMM packaging used 30 pins, with later models using 72 pins. The 30-pin modules supported in 8-bit wide address bus, whereas the 72-pin modules supported a 32-bit wide address bus. Therefore, in a Pentium class system using 72-pin SIMMs, you had to install the memory modules in matching pairs. This is because the Pentium class processor has a 64-bit data bus.

Figure 44: 30-pin SIMM with parity.

 


One easy way to Identify a 72-pin SIMM is the notch that separates the two sets of connectors on the bottom edge of the module (see Figure 45 below).

SIMMs

SIMMs
come in 30-pin and 72-pin modules. In a Pentium-class system, it takes two 72-pin SIMMs to make a bank of memory.


To install a SIMM module, place the bottom edge of the module into the socket at a 45° angle, and rotate the module until is at a right angle to the motherboard. When the module is in place, you will hear a small clicking noise as the two metal spring clips pop into place in front of the module, holding it in place.


Figure 45: 72-pin SIMM.

 


Due to the limitations of most chipsets and the overall real estate that a socket takes up on the motherboard, the industry created a new memory packaging technology, called a Dual In-line Memory Module, or DIMM.


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Dual Inline Memory Module (DIMM)
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