Hardware Reference
In-Depth Information
DDR2, the true clock speed is half the effective rate, which is technically expressed in million
transfers per second (MTps).
Table 6.9
shows the JEDEC-approved DDR3 module types and
bandwidth specifications.
Table 6.9. JEDEC Standard DDR3 Module (240-Pin DIMM) Speeds and Transfer Rates
The fastest official JEDEC-approved standard is DDR3-2133, which is composed of chips that run at
an effective speed of 2,133MHz (really megatransfers per second), resulting in modules designated
PC3-17000 and having a bandwidth of 17,066MBps. However, just as with DDR and DDR2, many
manufacturers produce nonstandard modules designed for overclocked systems. These are sold as
modules with unofficial designations, clock speeds, and performance figures that exceed the standard
ratings.
Table 6.10
shows the popular unofficial DDR3 speed ratings I've seen on the market. Note that
because the speeds of these modules don't conform to the standard default motherboard and chipset
speeds, you won't see an advantage to using them unless you are overclocking your system and your
motherboard supports the corresponding overclocked processor and memory settings that these
modules require. In addition, because these modules use standard-speed chips that are running
overclocked, they almost always require custom voltage settings that are higher than the 1.5V that
standard DDR3 memory uses. For system stability, I generally don't recommend using overclocked
(higher voltage) memory, instead preferring to use only that which runs on the DDR3 standard 1.5V.
Table 6.10. Overclocked (Non-JEDEC) DDR3 Module (240-Pin DIMM) Speeds and Transfer
Rates
