DDR SDRAM – A First Glance

DDR SDRAM – A First Glance

Like most of you, I’ve been waiting to see what DDR SDRAM really has to offer over PC133 SDRAM, and also to see if there will be differences in performance between chipsets. And as always, I’m also interested in the performance difference between an Athlon and Pentium III based system. There has been a lot of market hype over the last few months on this issue. Is DDR SDRAM really worth holding off your purchase? Is it really worth investing in new memory? What does it mean in ‘realworld’ use – those programs you and I use every day?

First – what is DDR SDRAM? Basically it’s SDRAM memory that has the ability to perform two operations per cycle, or ‘Double Data Rate’, instead of just one like standard SDRAM memory. Does that mean it’s twice as fast? Well no, there are many other issues that also affect memory performance. For more detailed info on memory and DDR take a look at these links as well as some of the memory articles linked from the front page…

http://www.via.com.tw/company/ddrzone.htm

http://www.teamddr.com/

http://www.crucial.com/ddr/index.asp

As when EDO replaced FP memory, SDRAM replaced EDO and RDRAM tried to replace SDRAM, or even when PC133 supplanted PC100 SDRAM, I didn’t expect to see a significant performance improvement with any of them. As expected, what we saw was a small incremental difference. But what we did see was memory technology that was then able to keep up with newer chipset and CPU technology: Higher bandwidth to go with ever faster CPU’s and Front Side Bus’s. As an example did we really see any difference between EDO and SDRAM when using an Intel TX chipset and a Pentium 233MX? No, but try to imagine using EDO at 66MHz with today’s PIII and Athlon CPU’s. Will the same thing go for DDR, e.g., not a huge gain in system performance, just a progressive step? There is only one way to find out – do some comparison testing.

To test, I ran two different PC133 SDRAM PIII Mainboards – a VIA 694X and Intel 815E along with one PC133 Athlon Mainboard, and compared them with two DDR SDRAM Mainboards – a PIII VIA based Apollo Pro 266 and an Athlon based AMD 761. I’d hoped to have an Ali MAGiK 1 based Athlon DDR and VIA KT133A 266MHz FSB Motherboard’s to test also, but haven’t been able to get my hands on them yet, so the Athlon DDR test is limited to 200MHz.

The following benchmarks were run under Windows 98 SE with the latest chipset drivers installed, 128MB of memory, a Cardex GeForce II MX 32MB AGP video card and a WD 200BB ATA/100 7200 RPM HD. Windows was set at 1024×768/64K @ 85Hz. All tests were run 3 times and were rejected if not within 3%, then the best of the 3 was used. The particular motherboard models were chosen because they all use today’s current chipsets and support (in the case of the PIII) 133MHz FSB and/or memory at 133MHz (except the AMD 761 based GA7DX – it runs the memory at 100MHz (or PC1600) if using a 100MHz host clock). Also the VIA Apollo Pro 266 motherboard is a pilot run part , subject to improvements as a production part, and the AMD 761 is one of the first so it also may improve with age.

I don’t know about you but I don’t see much difference at all in those results: DDR vs. SDRAM, Chipset vs. Chipset, or Athlon vs. PIII. In reality they all perform about the same, though the results do not include an Athlon using PC2100 memory.

Does that mean DDR is not worth buying or waiting for? I’d say, no that is not true. What is missing here is a close look at DDR vs. SDRAM using different speed CPU’s and specific applications. What we may see is that as CPU speeds get higher (like 1.2 or 1.5GHz) the system’s performance will be limited with SDRAM due to it’s lower bandwidth, and that DDR will start to shine because it has a higher bandwidth. We may also see specific applications that perform better with higher memory bandwidth, especially with faster CPU’s. You also need to remember that DDR is tomorrow’s memory, so if you want the latest technology it would be a good choice. And don’t forget, even though things like DDR, AGP, ATA/100 and other advancements don’t amount to a significant gain all on their own, using all of latest technology may add up to a significant gain.

DDR SDRAM is still in its infancy. Other than buying an AMD 760 based system, you can’t readily buy a DDR motherboard right now. Some AMD 760 based motherboard’s are just now hitting the market, but DDR capable motherboard’s based on VIA and Ali (and don’t forget about SiS) wont be on the market for at least a few more weeks, and wont be mainstream for at least a few months. Expect to see gains in performance via BIOS updates, drivers and maybe even chipset revisions as manufactures learn the new technology.