Compaq 850 manual Memory Subsystem, Sdram Interface Rdram Interface Dual Channel, Dimm Rdram

Technical Reference Guide

3.3MEMORY SUBSYSTEM

The 82850 MCH features Direct Rambus technology and supports two Rambus channels, each channel supporting up to two Rambus DRAM modules (RIMMs). Direct Rambus technology provides a significant improvement in performance over DRAM/SDRAM memory designs and allows the system memory to keep pace with increasing processor performance. Rambus technology implements RDRAM devices accessed over a channel specifically designed for high speed operations.

As shown in Figure 3-3, the conventional DRAM-based memory interface with a transfer rate of 66, 100, or 133 MHz increases bandwidth by widening the data bus. With the current top speed of 133 MHz, a 64-bit SDRAM interface achieves a maximum transfer rate of 1.0 GB/s.

SDRAM

Memory

Controller

Byte 0

Byte 1

Byte 2

Byte 3

Byte 4

Byte 5

Byte 6

Byte 7

DIMM

RDRAM

Memory

Controller

Byte 0

Byte 1

Byte 2

Byte 3

Ch 1

RIMM

Ch 2

RIMM

SDRAM Interface	RDRAM Interface (Dual Channel)
64-bit Path	32-bit Path
8 bytes @ 133 MHz = 1.0 GB/s	4 bytes @ 400 MHz = 3.2 GB/s (see text)

Figure 3–3.SDRAM/RDRAM Bandwidth Comparison

Although a Rambus channel handles only two bytes per transfer, data is clocked on both the rising and falling edges of the clock signal, allowing a 400-MHz clock to provide an effective speed of 800 MHz and resulting a transfer rate of 1.6 GB/s. Doubling the number of channels doubles the throughput. These systems feature dual-channel RDRAM architecture that provides a maximum transfer rate of 3.2 GB/s.

Compaq Deskpro EXS and Workstation 300 Personal Computers 3-5

Featuring the Intel Pentium 4 Processor

First Edition - December 2000