Hardware Reference
In-Depth Information
faster unofficial overclocked modules were produced), whereas DDR2 starts at 400MHz and goes up
to an official maximum of 1,066MHz.
JEDEC began working on the DDR2 specification in April 1998 and published the standard in
September 2003. DDR2 chip and module production actually began in mid-2003 (mainly samples and
prototypes), and the first chipsets, motherboards, and systems supporting DDR2 appeared for Intel
processor-based systems in mid-2004. At that time, variations of DDR2 such as G-DDR2 (Graphics
DDR2) began appearing in graphics cards as well. Mainstream motherboard chipset support for
DDR2 on Intel processor-based systems appeared in 2005. Notable for its lack of DDR2 support
through 2005 was AMD, whose Athlon 64 and Opteron processor families included integrated DDR
memory controllers. AMD processor-based systems first supported DDR2 in mid-2006, with the
release of socket AM2 motherboards and processors to match. (AMD's Socket F, otherwise known
as 1207 FX, also supports DDR2 memory.)
Note that AMD was almost two years behind Intel in the transition from DDR to DDR2. This is
because AMD included the memory controller in its Athlon 64 and all subsequent processors, rather
than incorporating the memory controller in the chipset North Bridge, as with the more traditional
Intel designs. Although there are advantages to integrating the memory controller in the CPU, one
disadvantage is the inability to quickly adopt new memory architectures because doing so requires
that both the processor and processor socket be redesigned. However, with the release of the Core i-
Series processors in 2008, Intel also moved the memory controller from the chipset into the
processor, thus putting Intel and AMD in the same situation in terms of memory architecture.
In addition to providing greater speeds and bandwidth, DDR2 has other advantages. It uses lower
voltage than conventional DDR (1.8V versus 2.5V), so power consumption and heat generation are
reduced. Because of the greater number of pins required on DDR2 chips, the chips typically use fine-
pitch ball grid array (FBGA) packaging rather than the thin small outline package (TSOP) chip
packaging used by most DDR and conventional SDRAM chips. FPGA chips connect to the substrate
(meaning the memory module in most cases) via tightly spaced solder balls on the base of the chip.
Table 6.7
shows the various official JEDEC-approved DDR2 module types and bandwidth
specifications.
Table 6.7. JEDEC Standard DDR2 Module (240-Pin DIMM) Speeds and Transfer Rates
The fastest official JEDEC-approved standard is DDR2-1066, which is composed of chips that run at
an effective speed of 1,066MHz (really megatransfers per second), resulting in modules designated
