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Recommended Book
The Winn L. Rosch Hardware Bible (6th Edition)
By Winn L Rosch
Que
Price: $0.03

Home » Memory
Everything You Need to Know About DDR Dual Channel
Author: Gabriel Torres
Type: Tutorials Last Updated: May 4, 2005
Page: 4 of 6
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Memory Speeds

On the table below you see all official speeds for SDRAM, DDR-SDRAM and DDR2. DDR and DDR2 transfer two data per clock cycle, so its rated clock isn't its real clock, as it occurs with the external bus of CPUs from AMD. We listed DDR2-667 and DDR2-800 just as a reference, since these memory types are not available on the market yet.

Memory

Tecnology

Rated Clock

Real Clock

Maximum Transfer Rate

PC66

SDRAM

66 MHz

66 MHz

533 MB/s

PC100

SDRAM

100 MHz

100 MHz

800 MB/s

PC133

SDRAM

133 MHz

133 MHz

1,066 MB/s

DDR200

DDR-SDRAM

200 MHz

100 MHz

1,600 MB/s

DDR266

DDR-SDRAM

266 MHz

133 MHz

2,100 MB/s

DDR333

DDR-SDRAM

333 MHz

166 MHz

2,700 MB/s

DDR400

DDR-SDRAM

400 MHz

200 MHz

3,200 MB/s

DDR2-400

DDR2-SDRAM

400 MHz

200 MHz

3,200 MB/s

DDR2-533

DDR2-SDRAM

533 MHz

266 MHz

4,264 MB/s

DDR2-667

DDR2-SDRAM

667 MHz

333 MHz

5,336 MB/s

DDR2-800

DDR2-SDRAM

800 MHz

400 MHz

6,400 MB/s

As we've been saying, in order to achieve the top performance your PC is capable of giving you, you should match the memory speed with the CPU speed (it is ok if your memory is faster than your CPU external bus, the problem is the other way around).

Actually, if you have an AMD CPU you won't have problems. For instance, if you have an Athlon XP with 400 MHz (3,200 MB/s transfer rate) external bus just install DDR400 memories on your computer and it will work great since both the CPU and the memory will be running at the same speed grade (3,200 MB/s). You can use DDR Dual Channel to improve the performance, anyway, as we will be talking about on the next page.

Intel processors are a problem. You don't even need to have a state-of-the-art PC to have memory bottleneck. The 2.4 GHz Pentium 4 from Figure 2 would need a 4,264 MB/s memory and from the table above you can see that only DDR2-533 can provide that. If you have a newer CPU with 800 MHz external clock rate, you would need DDR2-800 memories on your PC – a memory type that was not even lauched yet!

That's why Intel is pushing DDR Dual Channel. With this technique memory bandwidth is doubled and you can match the CPU speed with memory speed.

So, specially with Intel processors, if you don't use Dual Channel Memories your PC will achieve a performance lower than it is capable of.

Pages (6): « 1 2 3 [4] 5 6 »
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