DDR3 continues the evolution of the DDR and DDR2 technologies to provide continued improvements in performance.
The DDR3 technology is now in mainstream production and is expected to take over from DDR2 as the largest segment of DRAM production shortly.
However, it does offer increased transfer rates of PC3-6400 (2.5 ns clock), PC3-8500 (1.875 ns clock), PC3-10600 (1.5 ns. Clock), and PC3-12800 (1.25 ns clock). Thus, this technology can be a great new outlook for system designs that are performance driven. DDR3 also saves power by lowering the power supply voltage to 1.5 volts. STEC plans to offer a low power 1.35V module in the future.
DDR3 doubles the bandwidth available to your system once again and runs twice as fast as DDR3. DDR3 works very similar to DDR2 except that twice the number of data bits compared to DDR2 (or four times the data bits when compared to DDR), are fetched internally to enable transferring the sequential data at twice the speed of DDR2. Like DDR2 the data is transferred on both the rising and falling edge of the clock cycle enabling DDR3 to literally double the data transfer rate of the original bus clock. For example; with DDR3 a memory running with a clock of 533 or 667MHz will yield an effective data rate of 1066 or 1333 mega-transfers per second (MTS), doubling the data rate.
DDR2 is an emerging technology that is currently only supported by a small number of the latest microprocessors. DDR3 DIMM modules are available in a variety of form factors including 240 DIMM, 204 So-DIMM, and 244 Mini-DIMM. These form factors are not interchangeable with the preceding DDR or DDR2 technology form factors.
DIMMs have several different options for providing signal buffering on the DIMM to improve the performance and allow the system to support more DIMMs in a system. The list below describes the different types of buffering that can be on a DIMM.
The Very Low Profile (VLP) DIMM was created to save height for space constrained systems, including blade servers and ATCA (Advanced Telecommunications Architecture) applications. The DIMMS are also 133.5mm wide and have the same pinout as the DDR, DDR2, and DDR3 full-sized DIMMs. However, these modules will typically have a height between 18-19mm. This shortened height allows the designer to use a vertical socket and still fit the DIMM into his constrained chassis space.
The So-DIMM is a shortened DIMM form factor that was created originally for use in notebook computers. This module has a width of 67.6mm and these will typically use a horizontal socket when designed into the system. The original So-DIMM was defined without ECC for use in notebooks. But additional versions that include ECC have been created for embedded, telecomm, and other applications that require additional reliability. The So-DIMM can come in versions with pin-counts of 144 pins (SDRAM), 200 pins (DDR and DDR2), and 204 pins (DDR3).
The mini-DIMM is a relatively new form factor that was invented to provide the benefits of a shortened DIMM length but still provide additional pin-count to support new features in the DDR2 technology. Mini-DIMMs are currently available for only DDR2 in a 244-pin module and will always include ECC. These modules are 82mm long. It is likely that future extensions to the DDR3 standard will also provide this form factor for DDR3 technologies.
The VLP mini-DIMM is a new form factor that combines the shorter length of the mini-DIMM with the shorter height of the VLP DIMM. This form factor is a good solution for highly space constrained systems that only need a small to moderate amount of memory. The typical size of a VLP mini-DIMM is 82 mm long with a height between 18-19 mm.
A Registered DIMM has a chip called a Register chip on the DIMM module that will latch and buffer the address lines. Because of this Register chip, the DRAM controller will only see one load for the address lines instead of the 9 or 18 or more loads that would be present if the addresses were routed to every DRAM chips. The lighter loading will allow the DRAM controller to drive more DIMMs and at faster speeds. This type of DIMM module is commonly used in servers where there may be 8 or 16 or more DIMMs in a system. Registered DIMMs are only offered in versions with ECC.
An Unbuffered DIMM has no buffering on the DIMM. The DRAM controller will drive the address lines directly to each chip on the DIMM and the DIMM outputs will be go from the DRAM chip to the DRAM controller. This type of DIMM is commonly used on desktop and laptop PCs where the total amount of memory is limited and only one or two DIMMs are used in a system. Unbuffered DIMMs can be offered in versions without or without ECC.
• Scalability of Speeds to Reach 1600 MT/s
• Available in both Unbuffered and ECC Registered Versions
• Provides the highest transfer rate performance
• 1.5 Volt operating voltage and 1.35 Volt for lower applications
• High density: Up to 8GB (up to 16GB soon)
• Available in 240 DIMM, 204 So-DIMM, and 244 Mini-DIMM form factors
Four standard operating frequencies for the DDR3 SDRAM Memory Module specification were developed to provide the use with the most suitable option: PC3-6400, PC3-8500, PC3-10600, and PC2-12800.
PC3-6400 memory module configurations utilize DDR3-800 components to achieve the highest performance, with a peak bandwidth of 6.4GB/s when used in systems operating on 400MHz memory clock frequency.
PC3-8500 memory module configurations utilize DDR3-1066 components to achieve the highest performance, with a peak bandwidth of 8.5GB/s when used in systems operating on 533 memory clock frequency.
PC3-10600 memory module configurations utilize DDR3-1333 components to achieve the highest performance, with a peak bandwidth of 10.6GB/s when used in systems operating on 667 memory clock frequency.
PC3-12800 memory module configurations utilize DDR3-1600 components to achieve the highest performance, with a peak bandwidth of 12.8GB/s when used in systems operating on 800MHz memory clock frequency.
