DRAM Technologies

As microprocessors and chipsets evolve, so do memory technologies. Since DRAM is still the primary type of memory used in the PC, it has had to adapt to keep pace. The result is that new DRAM technologies are created that improve on the previous DRAM technology in a sort of memory one-upmanship. Each new DRAM technology is based at least in part on a preceding DRAM technology, usually improving its organization, speed, and access method.

Some of the more common DRAM technologies are:

· Fast Page Mode (FPM) FPM DRAM, which is also known as non-EDO DRAM, is compatible with virtually all motherboards with bus speeds under 66MHz.

· Extended Data Out (EDO) EDO, the most common technology of DRAM, is slightly faster than FPM DRAM and is very common in Pentium and later PCs with bus speeds under 75MHz.

· Synchronous DRAM (SDRAM) SDRAM (pronounced “ess-dee-ram”) is synchronized to the system clock to read and write memory in burst mode. This type of DRAM is more common on systems with higher bus speeds.

· Burst Extended Data Out (BEDO) DRAM BEDO (pronounced “beado”) is EDO memory with pipelining technology added. Pipelining allows BEDO DRAM to transfer data and accept the next request from the CPU at the same time. BEDO DRAM is common on PCs with clock speeds of up to 66MHz.

· Enhanced DRAM (EDRAM) EDRAM (pronounced “ee-dee-ram”) is a combination of SRAM and DRAM used for Level 2 cache.

· Double Data Rate (DDR) SDRAM A special form of SDRAM that is designed for systems with bus speeds over 200MHz.

· Enhanced SDRAM (ESDRAM) ESDRAM (pronounced “ehs-dee-ram”) is actually SDRAM with a small built-in SRAM cache that is used to increase memory transfer times. It works with data bus speeds of up to 200MHz.

· Direct Rambus DRAM (DRDRAM) DRDRAM (pronounced “dee-are-dee-ram” or “Doctor DRAM”) is a proprietary DRAM technology developed by Rambus, Inc. (www.rambus.com) and Intel. DRDRAM, along with a similar approach, SLDRAM (Sync Link DRAM), is capable of supporting memory speeds of up to 800MHz.

· FRAM (ferroelectric RAM) FRAM (pronounced “fram”) has features of both DRAM and SRAM, which means it can store data even after its power source is removed.