Memory Modules Of Three Different Types

Memory modules can be defined as memory chips on a narrow circuit board. The memory chip contains dynamic random access memory integrated circuits.

Originally memory was installed in the system through individual chips or the dual inline package (DIP) chips. It was laborious and time consuming job to deal with DIP chips. As the system experienced thermal changes on heating and cooling, the chips crept out of their sockets leading to a 'chip creep' phenomena. This resulted in memory errors. Reseating the chips back into the sockets solved the problem of course, but it became labor intensive when a number of systems had to be supported.

A better alternative to prevent 'chip creep' was to solder the memory into the motherboard/expansion card. With this the connections became more stable, but there was another problem. If the chip went bad, it had to be de-soldered and a new one had to be re-soldered or even it was required to scrap the motherboard/memory card where the chip was installed. This turned out very expensive and memory troubleshooting became a difficult task. A chip that was both soldered and removable was required and that lead to a memory module called SIMM or the Single inline memory module. In desktop systems most commonly used are two main types of SIMMS, three types of DIMMS, and one type of RIMM. On the motherboard or on the memory card's special connectors, these small boards get plugged into. They are, in-fact soldered into the module and removing/replacing is virtually impossible. If any part fails, the entire module has to be replaced.

SIMMs are available in 30 pin or 72 pin physical types. The 30 pin has 8 bits and an option for 1 additional parity bit. The 72 pin has 32 bits plus an option for 4 additional parity bit. Both these versions can have chips on one side or both sides except that 30 pin SIMMs are physically smaller than the 72-pin version.

DIMMs (Dual Inline memory modules) are available in three main versions-Standard DIMMs with 168 pins with one notch on each side and two notches along the contact area. DDR DIMMs with 184 pins and two notches on either side and one offset notch along the contact area. DDR2 DIMMS with 240 pins with two notches on either side and one notch in the center of contact area. The DIMMs are dual inline because they have different signal pins located on each side of the module. They have many more pins than a SIMM with just 1" of additional length.

RIMM (Rambus in line memory modules) have different signal pins on each side. They are available in three physical types-a 16/18 bit version having 184 pins, a 32/36 bit version with 232 pins and a 64/72 bit version with 326 pins. All these plug into the same sized connector, but notches in the connectors vary. In the standard 16/18 bit RIMM there is one notch on each side and two notched located centrally in contact area.