Should ram speed match FSB speed

Acer / PH
January 1, 2007 at 19:09:36
Specs: Windows XP Pro, Celeron D 352
I am looking to increase my ram speed from 512MB to 1GB. Does the speed of the ram need to match the speed of the CPU FSB of 533MHZ?


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January 1, 2007 at 20:41:21
"I am looking to increase my ram speed from 512MB to 1GB"

You wouldn't be increasing the speed, you'd be increasing the amount.

"Does the speed of the ram need to match the speed of the CPU FSB of 533MHZ?"

On an Intel system, 533MHz FSB actually runs at 133MHz, so all you'd need to match up would be PC2100. But if your board supports dual channel mode, you'd need to get a 512MB stick that closely matches the specs of the one you already have. You may find that what you have is PC2700 & it may be 2 x 256MB rather than a single 512MB stick. The only way to know for sure would be to open the case & look.

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January 2, 2007 at 00:52:04

Use their tool to diagnose the memory installed.

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January 2, 2007 at 03:35:01
I think the poster is referring to Optimized.

For example I have 800MHz FSB and running 533MHz (PC 4200) RAM.
Would this machine not run better using 800MHz (PC 6400) RAM thereby matching the RAM speed to the FSB speed?

I believe it would but cannot say for sure.


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Related Solutions

January 2, 2007 at 06:07:09
On a P4 system, 533MHz FSB doesn't actually run at 533MHz, it runs at 133MHz. The bus is "quad-pumped" so 533MHz is more theoretical speed than actual.

When choosing RAM, you have to think in terms of bandwidth & bus speeds, not just bus speed alone. Remember that DDR & DDR2 RAM is "double-pumped", so when you see the RAM listed as DDR266 (for example), the actual bus speed is 1/2 of that, or 133MHz. And to calculate bandwidth, you simply multiply the theoretical bus speed by 8.

For CPUs:

400FSB (@100MHz) x 8 = 3200MB/sec bandwidth
533FSB (@133MHz) x 8 = 4267MB/sec
800FSB (@200MHz) x 8 = 6400MB/sec
1066FSB (@266MHz) x 8 = 8533MB/sec

For RAM:

DDR266 (@133MHz) x 8 = 2133MB/sec (PC2100)
DDR333 (@166MHz) x 8 = 2667MB/sec (PC2700)
DDR400 (@200MHz) x 8 = 3200MB/sec (PC3200)
DDR533 (@266MHz) x 8 = 4267MB/sec (PC4200 or PC4300)
DDR667 (@333MHz) x 8 = 5333MB/sec (PC5300)
DDR800 (@400MHz) x 8 = 6400MB/sec (PC6400)

So in the case of this system with a 533FSB CPU with 4267MB/sec bandwidth, you'd need 2 x PC2100 running @ 133MHz in dual channel mode to have a 1:1 bandwidth ratio. The P4 tends to perform better if the RAM has a slightly higher bandwidth than the CPU, so you'd be better off getting 2 x PC2700 running at 166MHz in dual channel mode.

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January 2, 2007 at 14:26:25

Thank you for the input.
In the case of:
800FSB (@200MHz) x 8 = 6400MB/sec
(or 200MHz quad pumped making 800MHz FSB?)
DDR800 (@400MHz) x 8 = 6400MB/sec (PC6400)
(or 200MHz quad pumped making 800MHz FSB?)
Isn't that a perfect match?

Crucial Part Number: CT567684
Module Size: 1GB kit (512MBx2)
Package: Ballistix Tracer 240-pin DIMM (with LEDs)
Feature: DDR2 PC2-6400
Configuration: 64Meg x 64
Error Checking: NON-ECC
Speed: 800
SDRAM Timings: 4-4-4-12
Specs: DDR2 PC2-6400 • 4-4-4-12 • UNBUFFERED • NON-ECC • DDR2-800 • 2.2V • 64Meg x 64

Or am I missing what you are saying. Appreciate the education.
To break it down a little further I am currently running PC4200 at 2x512=1GB. Would the noted Crucial memory (of 1GB), instead of what I have, be better than what I have for this machine with a FSB of 800MHz (200MHz quad pumped)? No?

Like the poster's matching the FSB would be optimimal by marrying the FSB to the bandwidth @6400MB/sec vs the RAM @4267MB/sec using PC4200.


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January 3, 2007 at 15:25:34
No - the easy way to set the ram is to increase the speed intill the boot time starts to increase. Find the sweet spot by simple rasing the volts ddr2 loves 2.1v, then decrease the latencys and increase the speed with practice you find the sweet spot with no testing needed!

Do not do this when loading os - turn the ram to exact rating sometimes extra volts is good sometimes not. If you get a logo error after os loading you need to change the ram settings.

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