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 6-3-3-3

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 6-2-2-2

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 2005.

DDR-SDRAM