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CPU Bus speed and RAM Frequency
Tone2b 
3/9/08 4:32:56 PM
Serf
Hi All,

I have a very n00b question. If your processor has a bus speed of 1333Mhz (for example the Intel Q9650), should you install RAM with a matching frequency (i.e. 1333MHz) or is it OK to install RAM with a frequency of 1600Mhz (in this case DDR3)?

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Shikimaru 
4/9/08 8:56:41 AM
Titan

You can actually use any RAM you want, within the realms of DDR2 and DDR3 of course. All that is required is that the RAM and CPU run in a ratio with the FSB.

When the CPU says that it has a bus speed of 1333 MHz, that is actually the FSB speed multiplied by a number. For instance, 1333 could be a bus of 333MHz multiplied by 5.

For example, I own a E8500 with the stock speed of 3160MHz with a 1333 FSB. The bus runs (at stock) at 333MHz at a multiplier of 9.5. The FSB has a multi of 5 and the ram could run at 999MHz with a multi of 3, but it doesn't, it runs on a multi of 2 on 266MHz. This gives it a speed (DDR) of 1066MHz

Now i think i have all the technical stuff right, i'll just wait for someone to come and correct me ;)


Edited by Shikimaru: 4/9/2008 8:57:06 AM

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bu14-1 
4/9/08 1:25:29 PM
Primarch

I thought I heard that with the Intel setups, there was no point in having the frequency above 800MHz, but I would have thought this would change with the motherboard/chipset. Anyone know about this?

Thanks.

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Shikimaru 
4/9/08 3:52:59 PM
Titan

Quote by bu14-1
I thought I heard that with the Intel setups, there was no point in having the frequency above 800MHz, but I would have thought this would change with the motherboard/chipset. Anyone know about this?

Thanks.



Frequency of what?

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Quote by Catmosphere
Know thyself



c0nc0n 
4/9/08 9:51:05 PM
Champion

333 * 4 = 1333

Not 5. All intel FSB are quad pumped

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Shikimaru 
5/9/08 1:16:48 AM
Titan

Quote by c0nc0n
333 * 4 = 1333

Not 5. All intel FSB are quad pumped



Whoops lol

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Quote by Catmosphere
Know thyself



tantryl 
5/9/08 9:48:58 AM
SuperHero
Immortal


One more time.

Intel CPU FSBs are advertising as "quad pumped". In relation to the FSB they're really 1/4 of what they advertise.

All forms of DDR are "double data rate". In relation to the FSB they're really 1/2 of what they advertise.

So if your CPU FSB is "1333MHz" (really 333MHz) then your RAM should be "667" (really 333MHz) or above.

Intel's current Core architecture doesn't get a big performance boost out of higher MHz RAM than it's FSB. So for the vast majority of people the well priced DDR2-800 is the best buy at the moment.

If you spend the extra $400ish on DDR3-1333 or DDR3-1600 then you'll get a performance improvement of, in most cases, less than 5%. Money you would have been better off spending on a better CPU or graphics card that would show a real performance gain.

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Fat_Bodybuilder 
5/9/08 7:35:06 PM
Titan

Quote by Shikimaru
You can actually use any RAM you want, within the realms of DDR2 and DDR3 of course. All that is required is that the RAM and CPU run in a ratio with the FSB.

When the CPU says that it has a bus speed of 1333 MHz, that is actually the FSB speed multiplied by a number. For instance, 1333 could be a bus of 333MHz multiplied by 5.

For example, I own a E8500 with the stock speed of 3160MHz with a 1333 FSB. The bus runs (at stock) at 333MHz at a multiplier of 9.5. The FSB has a multi of 5 and the ram could run at 999MHz with a multi of 3, but it doesn't, it runs on a multi of 2 on 266MHz. This gives it a speed (DDR) of 1066MHz

Now i think i have all the technical stuff right, i'll just wait for someone to come and correct me ;)


Edited by Shikimaru: 4/9/2008 8:57:06 AM



Hmmm... Lets review this :P

1333 / 333 = 4.

Intel Processors, since the days of the P4, have a quad pumped FSB, meaning the bus speed times 4.

Not sure how you got to 1066 from 266 x 2. The Bus speed which controls the FSB, the CPU clock speed, also controls the RAM speed, and basically, natively is multiplied by 2. However in modern day systems you are able to multiply that to give you a higher RAM multiplier, using ratios and RAM multipliers. So you could have a bus speed of 333, and the memory should natively be running at 533MHz due to DDR (Double Data Rate) but you can change the RAM to have an effective clock speed of 1066 via using a memory multiplier of x4 (giving you 1066MHz).

The Bus speed, times the CPU multiplier give you the CPU (effective) clock speed (respectively). So the 333MHz bus speed will be mutliplied by 9 to give you an effective clock speed of 2997MHz or 3GHz (rounded up).

:-)

Now I'll read Tanty's post :-)

Cheers




Quote by c0nc0n
333 * 4 = 1333

Not 5. All intel FSB are quad pumped



Only from the P4s, the P3s etc were double pumped :P

Cheers





Edited by Fat_Bodybuilder: 5/9/2008 7:37:09 PM

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Tone2b 
5/9/08 7:44:51 PM
Serf
Thanks everyone. Valuable information

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