What is a Dual in-Line Memory Module?

The dual in-line memory module (DIMM) is a type of random access memory (RAM) utilized in various computers. Each module may utilize a number of what are known as a dual in-line package integrated circuits. Working in concert, these integrated circuits provide a way for computers to quickly write, read, and rewrite information in a dynamic manner.

Integrated circuits are simply miniaturized circuits that exist on the surface of a substrate material, such as silicon. Commonly known as microchips, the dual in-line package variety of integrated circuits can be recognized by their flat, rectangular shape. They also have two parallel rows of connector pins.

There are many different types of dual in-line memory module, each of which can have a different number of pins. These may range in number from 72 to 240, and typically dictate which type of DIMM the unit is. A DIMM with 72 pins may be known as a SO-DIMM, which stands for small outline dual in-line memory module. These relatively small RAM modules may be found in laptops, certain high-end printers, and PCs with small form factor mother boards. They are the smallest of the DIMMs, allowing them to be used in applications where space is a concern.

In addition to having different numbers of pins, many DIMMs have keyed notches that enable flawless installation. Since these notches are in different locations along the bottom of the DIMM, and may differ in number between one and three, it is generally impossible to install the wrong DIMM for any given application. By observing the location and number of the notches, it may be possible to determine whether the RAM module is correct before installation is even attempted.

The difference between the dual in-line and the single in-line memory module (SIMM) it replaced is that most DIMMs utilize a 64 bit bus width, while SIMMs only had a 32 bit data path. At one time processors with 32 bit bus widths were prevalent, but the introduction of 64 bit data path processors required SIMMs to be installed in matching pairs to add up to a total of 64 bits. The introduction of DIMMs allowed a single RAM module to be used in place of two SIMMs in these applications.

Dual in-line memory modules have gone through many evolutions in design since they were first introduced in the early 1990s. Subsequent generations of DIMMs, such as Double Data Rate (DDR), DDR2, and DDR3, all increased the amount of memory each module could contain, while also increasing the speed at which they could be written to and read.