What is DIMM?

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What is DIMM?
DIMM stands for Dual In-Line Memory Module. It contains a series of Random Access Memory (RAM) chips on a circuit board, and is connected to the motherboard with a 168-pin connector. Earlier memory modules were called SIMMS or Single In-Line Memory Module which had a 32-bit data path and required a 72-pin connector to the motherboard. In contrast, DIMM is actually a double SIMM with 64-bit data path. In the past, SIMMs were used in pairs to maximize the CPU’s processing power. DIMMs were created to specifically correct this inefficiency in installing memory modules.

DIMMs are becoming today’s standard memory modules for use in personal computers, high-end workstations, and servers. They come in various standard sizes called “form factors”. Older DIMMs usually range from 1.5 to 1.7 inches. When rack-mounted servers became popular, newer DIMM versions had to be squeezed into narrow spaces inside the computers, eventually trimming the standard size to 1.2 inches. With servers getting smaller, “very low profile” form factors were developed and the profile height was even lowered to 0.72 inches. There are also modules called SODIMM or “Small Outline DIMM” which are mainly used for notebooks and netbooks. Other popular form factors are the Mini-DIMM and the VLP Mini-DIMM.

There are also DIMMs that can implement error detection and correction. These are known as ECC DIMMs or “Error Correction Code DIMMs”. Most commonly used are SECDED (Single Error Correct – Double Error Correct) schemes. This type of scheme uses an extra 9th bit for every data byte.

DIMMs also come in two voltages: 3.3volts and 5.0volts. Versions can also be buffered or unbuffered. It is essential to have the correct DIMM for your machine, as the variations in voltages and buffer system yield to four different combinations. Today, the standard being used are unbuffered DIMMs with 3.3 volts.

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