168 Pin DIMM

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A dual inline memory module (DIMM) consists of a number of memory components (usually black) that are attached to a printed circuit board (usually green). The gold or tin pins on the bottom of the DIMM provide a connection between the module and a socket on a larger printed circuit board. The pins on the front and back of a DIMM are not connected, providing two lines of communication paths between the module and the system.

168-pin DIMMs are commonly found in Pentium and Athlon systems. Each 168-pin DIMM provides a 64-bit data path, so they are installed singly in 64-bit systems. 168-pin DIMMs are available in FPM, EDO, 66MHz SDRAM, PC100 SDRAM, and PC133 SDRAM. When upgrading, be sure to match the memory technology that is already in your system.

The number of black components on a 168-pin DIMM may vary, but they always have 84 pins on the front and 84 pins on the back for a total of 168. 168-pin DIMMs are approximately 5.375" long and 1.375" high, though the heights may vary. They have two small notches within the row of pins along the bottom of the module.

Dual In-line Memory Modules, or DIMMs, closely resemble SIMMs. Like SIMMs, most DIMMs install vertically into expansion sockets. The principal difference between the two is that on a SIMM, pins on opposite sides of the board are "tied together" to form one electrical contact; on a DIMM, opposing pins remain electrically isolated to form two separate contacts.

168-pin DIMMs transfer 64 bits of data at a time and are typically used in computer configurations that support a 64-bit or wider memory bus. Some of the physical differences between 168-pin DIMMs and 72-pin SIMMs include: the length of module, the number of notches on the module, and the way the module installs in the socket. Another difference is that many 72-pin SIMMs install at a slight angle, whereas 168-pin DIMMs install straight into the memory socket and remain completely vertical in relation to the system motherboard.

In late 1996, SDRAM began to appear in systems. Unlike previous technologies, SDRAM is designed to synchronize itself with the timing of the CPU. This enables the memory controller to know the exact clock cycle when the requested data will be ready, so the CPU no longer has to wait between memory accesses. SDRAM chips also take advantage of interleaving and burst mode functions, which make memory retrieval even faster. SDRAM modules come in several different speeds so as to synchronize to the clock speeds of the systems they'll be used in. For example, PC66 SDRAM runs at 66MHz, PC100 SDRAM runs at 100MHz, PC133 SDRAM runs at 133MHz, and so on. Faster SDRAM speeds such as 200MHz and 266MHz have also been developed.

FAST PAGE MODE (FPM)

At one time, FPM was the most common form of DRAM found in computers. In fact, it was so common that people simply called it "DRAM," leaving off the "FPM". FPM offered an advantage over earlier memory technologies because it enabled faster access to data located within the same row.

EXTENDED DATA OUT (EDO)

In 1995, EDO became the next memory innovation. It was similar to FPM, but with a slight modification that allowed consecutive memory accesses to occur much faster. This meant the memory controller could save time by cutting out a few steps in the addressing process. EDO enabled the CPU to access memory 10 to 15% faster than with FPM.