Memory - Upgrading and Repairing PCs - page 329

PC2-8500 having a bandwidth of 8,533MBps. However, just as with DDR, many of the module
manufacturers produce even faster modules designed for overclocked systems. These are sold as
modules with unofficial designations and performance figures that exceed the standard ratings. Table
6.8 shows the popular unofficial speed ratings I've seen on the market. Note that because the speeds
of these modules are beyond the standard default motherboard and chipset speeds, you won't see an
advantage to using these unless you are overclocking your system to match.
Table 6.8. Overclocked (Non-JEDEC) DDR2 Module (240-Pin DIMM) Speeds and Transfer
Rates
Typically, you can find DDR2 modules rated between CL 3 and 6.
DDR3 SDRAM
DDR3 enables higher levels of performance along with lower power consumption and higher
reliability than DDR2. JEDEC began working on the DDR3 specification in June 2002, and the first
DDR3 memory modules and supporting chipsets (versions of the Intel 3x series) were released for
Intel-based systems in mid-2007. Due to initial high cost and limited support, DDR3 didn't start to
become popular until late 2008 when Intel released the Core i7 processor, which included an
integrated tri-channel DDR3 memory controller. In early 2009, popularity increased when AMD
released Socket AM3 versions of the Phenom II, the first from AMD to support DDR3. In 2009, with
full support from both Intel and AMD, DDR3 finally began to achieve price parity with DDR2,
causing DDR3 to begin to eclipse DDR2 in sales.
DDR3 modules use advanced signaling techniques, including self-driver calibration and data
synchronization, along with an optional onboard thermal sensor. DDR3 memory runs on only 1.5V,
which is nearly 20% less than the 1.8V that DDR2 memory uses. The lower voltage combined with
higher efficiency reduces overall power consumption by up to 30% compared to DDR2.
The 240-pin DDR3 modules are similar in pin count, size, and shape to the DDR2 modules; however,
the DDR3 modules are incompatible with the DDR2 circuits and are designed with different keying to
make them physically noninterchangeable.
DDR3 modules are available in speeds of 800MHz (effective) and higher. Just as with DDR and