What’s a DIMM?

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DIMM is a type of computer memory used in Pentium or higher computers. It consists of a circuit board that holds SDRAM or DDR SDRAM chips and transmits data to the processor 64 bits at a time. DIMMs come in several types and sizes, and are not interchangeable. Installing DIMMs is a simple process, but it is important to verify the type before replacing or upgrading.

DIMM, which stands for dual in line memory module, is a type of computer memory used in Pentium or higher computers. A DIMM consists of a small circuit board that holds four or nine (with parity) synchronous dynamic random access memory (SDRAM) or double data rate (DDR) SDRAM chips per side. The pin connection board fits into a socket on the motherboard and transmits data to the processor 64 bits at a time. DIMMs come in 64-bit Error Correcting Code (ECC) modules or 72-bit modules with parity. There are several types of DIMMs; however, the three main types are SDRAM, DDR SDRAM, and DDR2 SDRAM. DIMM sizes range from 64 Megabytes (MB) for older SDRAM to 128 Gigabytes (GB) or more per DDR2 RAM module.

Of the different types of DIMMs, 168-pin SDRAM is known as the original DIMM and had clock and data speeds up to 133 Megahertz (MHz). These modules had one notch on each side and two notches on the connecting edge. DDR 184-pin and DDR240 2-pin memory share a similar architecture, with two notches on each side and one notch along the connecting edge. DDR memory has clock speeds up to 200 MHz and double the data rate of SDRAM. DDR2 memory has clock speeds up to 200 MHz and data rates that quadruple SDRAM. Other types include DDR3 memory, a faster and more expensive variety, and laptop SO-DIMMs.

By about the year 2000, DIMMs had replaced SIMMs, or single-in-line memory modules, as the computer memory standard in Pentium systems. Unlike SIMMs, which contained 16- or 32-bit data paths and required adding pairs to fully utilize a Pentium PC’s 64-bit data path, the data transfer rate of a single DIMM scaled with the bus width Pentium processor data perfectly, thus eliminating the need for pairs.

Another difference between the two types of computer memory lies in the way the link edges work. The connecting edges on both sides of a DIMM point to different circuits that respond differently to electrical signals. This adds more power to a computer system as more communication lines are possible to the processor. A SIMM, on the other hand, carries the same connectors on each side of the module and can handle a communication line with the processor.

While installing DIMMs is a fairly simple process, DIMM memory types are not interchangeable with each other. Always refer to your motherboard or PC manuals to verify the type before replacing DIMMs or performing memory upgrades. First, shut down and unplug your computer. Remove the case and look for the memory slots on the motherboard. DIMM slots are usually black and located close to the processor. Dissipate extra static electricity by touching a metal object.

Next, set the eject clips to the “down” position. Holding the memory module by the edges to avoid direct contact with the pins, align the notches on the connecting edge against the keys in the socket so they match. Press the module into place until it clicks and both ejectors engage the module. Replace the computer cover, reconnect the cables, and turn on the computer. In most cases, the system should recognize the new memory.




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