Ddr-3; Module Naming Convention And Peak Bandwidth - Compaq BL10e - HP ProLiant - 512 MB RAM Overview

DDR-3

DDR-3, the third-generation of DDR SDRAM technology, makes further improvements in bandwidth
and power consumption. Manufacturers of DDR-3 started with 90 nm fabrication technology and are
moving toward 70 nm as production volumes increase. DDR-3 operates 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 DIMMs
can reduce power consumption by up to 30 percent compared to DDR-2 DIMMs operating at the
same speed. DDR-3 DIMMs use the same 240-pin connector as DDR2 DIMMs, but the notch key is in
a different position (Figure 14).
Figure 14. DDR-3 DIMM with 240-pin interface
To increase performance and reduce power consumption of DDR-3, designers made several key
enhancements:
An 8-bit prefetch buffer stores more data before it is needed than the 4-bit buffer for DDR2 does.
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 reduces power consumption even further than 1.8 V signaling for DDR-2.
A thermal sensor integrated on the DIMM module signals the chipset to throttle memory traffic to the
DIMM if DIMM temperature exceeds a programmable critical trip point.

Module naming convention and peak bandwidth

Table 2 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. However, due to confusion 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).
Manufacturers of DDR-3 SDRAM DIMMs are producing two types of DIMMs: Unbuffered DIMMs
(UDIMM) and Registered DIMMs (RDIMM). UDIMMs represent the most basic type of memory module
and offer lower latency and (relatively) low power consumption but are limited in capacity.
Unbuffered DIMMs with ECC are identified with an E suffix in the manufacturer's module name
(example PC3-8500E). UDIMMs are applicable for systems with low DIMM counts and where large
memory capacities are not required.
RDIMMs offer larger capacities than UDIMMs and include address parity protection. Registered
DIMMs are identified with an R suffix in the module manufacturer's name (example PC3-8500R).
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