Dynamic Random Access Memory (DRAM) CS 350 Computer Organization Spring 2004 Aaron Bowman Scott Jones Darrell Hall

DYNAMIC RANDOM ACCESS MEMORY (DRAM) Simple DRAM Fast Page Mode (FPM) DRAM Extended Data Out (EDO) DRAM Burst Extended Data Out (BEDO) DRAM Synchronous DRAM (SDRAM) Rambus DRAM (RDRAM) Double Data Rate (DDR) DRAM

Simple DRAM  Memory system directly connected to the CPU and was the basic architecture that was most commonly used by system designers on early microcomputer systems  Simplest system to design and also the least expensive  Preferred type for systems with a processor that operates at speeds lower than 16 MHz  In the late 1980s processors began to operate at speeds faster than that so a new architecture was necessary.

Fast Page Mode (FPM) DRAM  Continually accesses memory from the same row of RAM without having to specify the row each time  Burst cycle timing as fast as  Not only does this increase the access speed, but it also lowers power requirements.  Rarely used because it is slower than newer memory types

Extended Data Out (EDO) DRAM  Often called Hyper Page Mode DRAM  Modified timing circuits that allow it to begin one memory access before the previous one has finished  Burst cycle timing as fast as  With no price difference and the speed gained using EDO DRAM, there was no reason to choose FPM DRAM over EDO DRAM.

BEDO DRAM Advantages over EDO Improved Cycle time with address counter on chip Optimized use of four set data burst Disadvantage Not Synchronized with CPU Not keep up with buses faster the 66 MHz Built on asynchronous bus compared to SDRAM

SDRAM First type of DRAM to run synchronous with the CPU This allowed SDRAM to run at faster speeds Comes in SIMMs and DIMMs SIMMs need two modules DIMMs need one module

RDRAM RDRAM is short for Rambus DRAM. Created by the Rambus company. RDRAM can transfer data up to 800 MHz.

A single RDRAM is able of providing up to 1.6 GB per second data transmission even though it has a low pin count. Turnaround latency is comparatively faster, at 12 to 23 nanoseconds. RDRAM equipped systems are more efficient and achieve lower latency over SDRAM. RDRAM

DDR-SDRAM DDR-SDRAM is short for Double Data Rate- Synchronous DRAM. SDRAM II and DDRAM are other names for DDR-SDRAM. Uses both the raising and falling edge of the clock signal for the transfer of data.

First generations peaked at 333 to 400 MHz with memory up to 512 Mbits. Second-generations DDR II is capable of 400 MHz. Third generation DDRs will offer even higher data rates due out late 2004 or early DDR-SDRAM