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

Module naming

Bus speed

Peak bandwidth

 

naming

convention

 

 

 

convention

 

 

 

 

 

 

 

 

DDR-1

DDR200

PC1600

100 MHz

1.6 GB/s

 

 

 

 

 

 

DDR266

PC2100

133 MHz

2.1 GB/s

 

 

 

 

 

 

DDR333

PC2700

166 MHz

2.7 GB/s

 

 

 

 

 

 

DDR400

PC3200

200 MHz

3.2 GB/s

 

 

 

 

 

DDR-2

DDR2-400

PC2-3200R

200 MHz

3.2 GB/s

 

 

 

 

 

 

DDR2-533

PC2-4300

266 MHz

4.3 GB/s

 

 

 

 

 

 

DDR2-667

PC2-5300

333 MHz

5.3 GB/s

 

 

 

 

 

 

DDR2-800

PC2-6400

400 MHz

6.4 GB/s

 

 

 

 

 

DDR-3

DDR3-800

PC3-6400

400 MHz

6.4 GB/s

 

 

 

 

 

 

DDR3-1066

PC3-8500

533 MHz

8.5 GB/s

 

 

 

 

 

 

DDR3-1333

PC3-10600

667 MHz

10.6 GB/s

 

 

 

 

 

 

DDR3-1600

PC3-12800

800 MHz

12.8 GB/s

 

 

 

 

 

14