Memory manufacturer Micron this week demonstrated the first system running DDR-II SDRAM to press and analysts.
DDR-II, which represents the next generation of memory, is seen as a necessary redesign to increase speeds as DDR-I runs out of steam. Broadband Internet access, 3D graphics, wireless communications, high-speed networking and higher processor clock rates are all driving the need for memory bandwidth and DDR-II is expected to be the next mainstream memory standard, although it is not expected to be widely available for at least another year.
Micron was not the first company to produce DDR-II memory -- Samsung said at the end of May that it had produced 512Mb DDR-II SDRAM modules, and expects to be in volume production of the new 512Mb DDR-II SDRAM device in late 2003. And although Micron's DDR-II chips are only 256Mb, the development of a working system is an important step toward building chipsets and motherboards that can support the new memory.
"We believe this is the first desktop PC with DDR-II memory," said Terry Lee, Micron's director of advanced technology, referring to the development system encased in a large Perspex case. With no chipsets currently available to support DDR-II memory, the system used a specially built PCI expansion board into which the memory modules plugged.
"This allows us to examine how robust the system is, how much timing margin we have," said Lee, adding that the development system would be shared with customers.
If any company is to produce hardware to support DDR-II, it will have a number of engineering challenges to overcome due to the fast data rates and low voltages demanded by the specification.
DDR-II memory enables data transmission speeds of 400Mbps on a 100MHz bus, and up to 600Mbps if the bus frequency is cranked up to 150MHz -- a scenario envisaged for high-speed networking applications. Micron's demonstration system enabled data transfer speeds of 533Mpbs.
Line voltages are also much lower in DDR-II systems than is necessary in current memory standards -- down from 2.5v to 1.8v -- meaning that signals are much more susceptible to interference and timing issues. Lower line voltages are necessary to make the memory interface better with logic chipsets, according to Lee.
One way the company has improved signal quality, said Lee, is by adding line terminators -- much like the ones used at the end of SCSI daisy chains. Line termination was introduced in DDR-I-based DDR266 memory modules in the form of resistors soldered into the memory modules; for DDR-II memory, the line termination is shifted onto the die, increasing signal quality further and resulting in potentially lower module costs in the long term.
Lee said that Micron expects to have a system with a DDR-II slot on the motherboard by the end of 2002. Echoing Samsung's estimation, Lee said he expected systems to ship with DDR-II in the second half of 2003, with volume shipments starting in early 2004.
However, there are still issues to work out with the standard, said Lee. "The standard for this memory is essentially fixed," he said. "But there is still a debate about how to do four slot memory banks for servers." PCs are likely to ship with just two DDR-II memory slots, said Lee; with 512Mb modules, this will provide 2GB of memory.
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