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DDR2 speeds get up to speed DDR2 speeds get up to speed
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Old 13th June 2005, 23:13   #1
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Default DDR2 speeds get up to speed

DDR2 SDRAM was kinda plagued with the real-life performance problem vs its DDR(1) predecessor since the fist Intel systems using it appeared late last year. Yes, the voltage is lower and yes the prices arean't that bad anymore, but generally, even the DDR2-533 at 3-3-3-8 at 1066MHz front side bus (FSB) had a hard time showing any measurable application performance increase over DDR1-400 at 2-2-2-5 on a 800MHz FSB.
And if you stick with the 800MHz FSB, like what are you supposed to do with the new Pentium D and Pentium EE dual-core Intel darlings? Well then, surprise surprise, if keeping the CPU and memory clock in sync, you have got to stick with DDR2-400 at something like 3-2-2-6 (if using Corsair 5400UL, the lowest-latency DDR-2 around right now), yet you'll still be slightly faster if you use the old DDR1-400. The 3200XL 2-2-2-5 DIMMs from the same vendor, for instance. Looks funny then - where's the technological advantage?

Well, there's another way now... use DDR2-800 instead, with double the bandwidth of th FSB, so still in sync, but total latency in ns reduced due to different settings, plus the remainder of the burst transfer goes of course in half the time. And there were quite a few such entries at this year Computex - from more than one vendor, that is.

According to the initial roadmaps a year ago, DDR2 was supposed to evolve to the DDR2-800 standard in 2006, followed by the next migration, to DDR3, which would start with the 1066 speed grade sometime in 2007.

Somehow, either someone used some secret sauce, or the real potential of DDR2 was discovered earlier. Every 'enthusiast oriented' memory vendor, absolutely every one, had DDR2-800 DIMMs on display. And most of them had these goodies shipping now, in fact. The latencies weren't that impressive, usually 5-5-5-15 or a bit better than that, and most could work at 5-4-4-12 or so, too - now remember, that would equal to a 2.5-2-2-6 DDR2-400, plus the bonus of the remaining burst transfer going at twice the speed... so yes, this would match even the fastest DDR1-400 in overall latency, plus give faster bursts.

Some of the vendors, like Corsair, OCZ, A-data and Transcend, showed, for the first time, DDR2-1066 units too. Wow, we crossed the gigglehurtz throughput chasm for the main system memory too, almost two years ahead of 'schedule'? In fact, these RAMs are so fast, bandwidth-wise, that you could start thinking of doing high-end graphics cards with multiple DIMM slots based on this memory, huh - the speeds are approaching the fastest graphics memory!

Corsair went a step further, and reduced the latency a bit too - to provide 5-4-4-9 for the DDR2-1066 setting, an ideal match to turbo charge Pentium 4 1066 MHz FSB machines, even if using just a single channel! If you're lucky, you could possibly also run this DIMM at 4-3-3-8 at DDR2-800 clock if using FSB800, again filling up the CPU bandwidth with just one DIMM.

Well, of course, not every board will run DDR2-800, not to mention DDR2-1066. Intel reference boards all stick with DDR2-667 maximum, but Abit and Asus, followed by MSI, Gigabyte and others, should run DDR2-800, and in many cases DDR2-1066, fine on their newest mobos based on Intel 955X and Nvidia SLI chipsets.

So, if you use them in dual-channel configuration, you may get something like 17 GB/s of total memory bandwidth in the system! That's twice that of Pentium 4 FSB 1066, in fact nearly three times that of Intel's current "Tiger 4" quad-CPU Itanium2 reference system.

So, unless able to drive the Pentium 4 FSB enormously upwards, with even 1250 FSB not an easy feat, and simultaneously having a plenty of PCI-E traffic to and from your Crossfire/SLI /whatever graphics card combo, there's actually little use for that spare bandwidth right now - besides a bit faster overall CPU memory transfers.

But again, it comes at no extra cost besides the memory cost, of course... so why not? After all, even the old DDR1 is still advancing: 2-2-2-5 DDR1-500 is the next round, assumingly for the interim Athlon64/Opteron memory speed update to sync the memory bus to 1 GHz HT throughput - both at 8 GB/s, before they also go DDR2 next year in the new sockets, and some vendors will even have DDR1-600 at 2-2-2-x timings... so that battle still goes on.

http://www.theinquirer.net/?article=23918
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Old 14th June 2005, 00:04   #2
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Quote:
DDR1-600 at 2-2-2-x timings
Whoever comes up with this will make a few easy dollars FAST and with more than 12-month window of opportunity
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