Second-Gen DDR SDRAM On The Horizon

cplcap writes "This story in The Register picks up on Samsung's new DDR-II Chips, pushing DDR's speed up to 533 Mb/s and a 4.2GB/s memory bus. Prototype 512MB DIMMs are being produced, and IBM has developed a chipset to take advantage of the speed. There's a little more meat in Samsung's official press release."

Comments

the big question is...

[Lumpy]

Is it a whole new form factor so everyone had to redesign the motherboards and to force incompatability with older systems??

This is important because industrial and corperate-mission-critical is older equipment. and an upgrade path for ram is still important.

Re:the big question is...

[ToLu the Happy Furby]

Is it a whole new form factor so everyone had to redesign the motherboards and to force incompatability with older systems??

The answer is...yes and no. DDR-II does have a new form factor, with 232 pins, as compared to the 184 currently used in a DDR (I) DIMM. Similarly, a DDR (I) DIMM has a bit more pins than the 168 found in an SDRAM DIMM.

However, this isn't such a big deal for the mobo makers; it's just a matter of putting on a different slot and different traces on the board. One of the things that has made the transition from SDRAM to DDR more "evolutionary" than a transition to (say) RDRAM would have been, is that the same chipset can control both SDRAM and DDR, because they use the same (or at least backwards-compatible) commands. It's not often mentioned on the hardware-enthusiast sites which are only interested in benchmarking the fastest stuff around, but just about every DDR chipset is also available with SDRAM. You need a different motherboard--because the slots are incompatible--but the cost to the mobo makers for offering both versions is pretty small.

In a similar vein, the commands for DDR-II are a superset of the DDR-I command set, such that DDR-II chipsets should very easily be able to detect and use DDR-I as well, just like DDR-I chipsets currently use SDRAM as well. Furthermore there is talk (dunno if it will happen) of releasing DDR-I DIMMs in the 232-pin DDR-II form factor; that way, one could buy a motherboard and use either DDR-II or DDR-I in it, with no problems. Of course old sticks of DDR-I will not fit, and the new ones will not fit in current DDR motherboards.

So, while such a scheme doesn't get rid of all the headaches of an incompatible upgrade path, it does address some, albeit more on the mobo producer end of things than on the IT inventory end of things. It is indeed a pain that, while SDRAM (and the SDRAM form factor) enjoyed around 4 years as the mainstream memory type, DDR-I will only be on top for 2 before DDR-II takes over. And DDR-II will be lucky to have 3 years before something pin-incompatible comes along to replace it.

On the other hand, the SDRAM -> DDR transition probably would have happened a year earlier if Intel hadn't tried to transition to RDRAM instead. And, meanwhile, being stuck with SDRAM for 4 years meant DRAM bandwidth only doubled (and actual performance did less than that) over a period when CPU clock speeds increased by a factor of 5 or so. I think the DRAM industry wants to make speed increases more frequent than they were a few years ago, even if this means more inconvenience for corporate IT departments.

This is important because industrial and corperate-mission-critical is older equipment. and an upgrade path for ram is still important.

I'm not sure what you mean here. As far as the upgrade path for greater RAM capacity goes, standard SDRAM and DDR-I will still be made and sold for quite some time, even if they will eventually be more expensive than their newer and faster brethren. EDO RAM is still being made and sold today.

If you mean an upgrade path for higher-performance, of course you can't just buy faster DRAM and expect it to speed up (or even work in) a system that was built to use a slower type. The system clock sets the DRAM speed, and unless the system has been validated to run at the new DRAM speed, doing so amounts to overclocking. An performance upgrade path for RAM is always going to require purchasing at least a new CPU module and accompanying memory bus, if not a new machine.

A few facts

[Anonymous Coward]

Intro: I am D. C. Sessions, and I'm the chair of JC-16 (one of the committees which participates in the DDR standard). Here are a few facts:

The two big reasons for the generational change are

• Voltage change: DDR II is going to 1.8 volts to allow thinner gate oxides and denser, faster devices.
• Internal timing. First-generation DDR has some architectural timing issues which make it impossible to go much beyond 333 in volume production.

Yes, this makes for backward-compatibility problems.

Yes, the Committee (JC-42.3) put a huge amount of work into making DDR-II as backward-compatible as possible

Yes, we're starting work on DDR-III. You'll have to wait until 2006 or so.

Target speeds for DDR-II were set at 600 MT/s for fully-loaded systems and 800 MT/s for embedded stuff like graphics.

The signal-integrity issues for DDR-II are ugly, but we met the margin specs with lots of conservativism thrown in, so once we get hands-on time with systems you'll probably see the numbers exceeded just as the original DDR targets were.

Flame away. You can get more info at JEDEC or Advanced Memory International.

Motherboard makers might just skip it.

[jefp]

DDR-II is basically equivalent to on-chip interleaving - the data path is clocked the same but twice as wide. Well, board makers are now doing motherboard-side DDR interleaving themselves - see recent boards based on the ServerWorks GC-LE or Intel E7500 chipsets. Some manufacturers might just decide not to bother with DDR-II.