HP 117755-003 740 Overzicht - Pagina 14

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DDR-3

DDR-3, the third-generation of DDR SDRAM technology, will make further improvements in bandwidth

and power consumption. Manufacturers of DDR-3 will initially use 90 nm fabrication technology and

move toward 70 nm as production volumes increase. DDR-3 will operate at clock rates from 400

MHz to 800 MHz with theoretical peak bandwidths ranging from 6.40 GB/s to 12.8 GB/s. DDR-3 is

expected to reduce power consumption by up to 30% compared to a DDR-2 DIMM operating at the

same speed. DDR-3 DIMMs are expected to use the same 240-pin connector as DDR2 DIMMs, but the

key notch will be in a different position.

To increase performance and reduce power consumption of DDR-3, designers made several key

enhancements, including:

• An 8-bit prefetch buffer, compared to the 4-bit buffer for DDR-2, storing more data before it is

needed.

• Fly-by topology (for the commands, addresses, control signals, and clocks) improves signal integrity

by reducing the number of stubs and their length. This feature requires the controller to support

"write leveling" on DDR-3 DIMMs.

• 1.5-V signaling (compared to 1.8 V for DDR-2) for lower power consumption

• A thermal sensor integrated on the DIMM module signals the chipset to throttle memory traffic to the

DIMM if its temperature exceeds a programmable critical trip point.

Module naming convention and peak bandwidth

Table 1 summarizes the various types of DDR-1, DDR-2, and DDR-3 SDRAM and their associated

naming conventions. Originally, the module naming convention for DDR-SDRAM was based on the

effective clock rate of the data transfer: PC200 for DDR SDRAM that operates at 100 MHz; PC266

for 133 MHz; and so forth. But after confusion arose over the Rambus naming convention, the

industry based the DDR-SDRAM naming convention on the actual peak data transfer rate in MB/s. For

example, PC266 is equivalent to PC2100 (64 bit * 2 * 133 MHz = 2.1 GB/s or 2100 MB/s).

Table 1. Summary of DDR SDRAM technologies

Type

Component

naming

convention

DDR-1

DDR200

DDR266

DDR333

DDR400

DDR-2

DDR2-400

DDR2-533

DDR2-667

DDR2-800

DDR-3

DDR3-800

DDR3-1066

DDR3-1333

DDR3-1600

Module naming

Bus speed

convention

PC1600

100 MHz

PC2100

133 MHz

PC2700

166 MHz

PC3200

200 MHz

PC2-3200R

200 MHz

PC2-4300

266 MHz

PC2-5300

333 MHz

PC2-6400

400 MHz

PC3-6400

400 MHz

PC3-8500

533 MHz

PC3-10600

667 MHz

PC3-12800

800 MHz

Peak bandwidth

1.6 GB/s

2.1 GB/s

2.7 GB/s

3.2 GB/s

4.3 GB/s

5.3 GB/s

6.4 GB/s

8.5 GB/s

10.6 GB/s

12.8 GB/s