A Bit About FSB and RAM

D

Dav0s

New member
Ok so many of you know that your FSB and your RAM speed are connected somehow yes? Many of you will also know what I am about to explain but some may not so I will continue.

The FSB (Front Side Bus) is the speed which many of the components connected to your motherboard run at. In order to overclock you must raise this FSB as one of the steps. Problem is that this also riases the speed of everything else in your system which can be a problem. The biggest problem is likely to be the RAM which is what I will cover in this guide.

Firstly you must know a bit about RAM speed. All RAM will have two aliases to check its speed. For example...

PC2700 - DDR333

The speed most useful to us is the DDR333 part. This tells us the RAMS recommended speed in relation to FSB.

Because DDR RAM (Double Data Rate) runs at twice the speed of the FSB you must divide this number by two to find the recommended maximum speed of the RAM. In our case the recommended maximum speed is 166FSB.

Now that you have the speed of your RAM you can judge how far it is being pushed by knowing your FSB. My celeron system runs stock at 133FSB and I have DDR333 ram. Therefore my 166FSB RAM is plenty enough for my FSB.

However this gets more complicated when we move on to overclocking. You need to buy faster RAM than your FSB if you want a successful stable overclock. For example if you have overclocked to have a 250FSB then you will need DDR500 RAM at least.

However Faster RAM will work fine in a slower machine.

It will simply run at the FSB speed which wil be slower than its recommended speed. It is a common myth among some noobs that you can only use the correct speed RAM in a system but this is not true.

Now we have covered a bit on the speed of RAM and basic overclocking I will just explain "Quad-Pumping" to you.

All intel CPU's are "quad-pumped" which means that they actually run at 4 times the speed of the FSB. It is kind of like DDR ram running at twice the speed of the FSB. So the afor mentioned 250FSB computer could also be referred to as running at a 1000FSB. When Intel quote specs for their processors they use the quad-pumped FSB so an 800FSB is actually running at 200FSB as far as the motherboard and BIOS are concerned.

I hope that this guide has helped you to understand the relationship between FSB/RAM and CPU speeds and this will also help you to overclock more efficiently and effectively.

Dave :)
 
DDR stands for Double Data Rate, so effectively any DDR- rating is 2x the actual MHZ speed.

The numeric part of DDR (DDR2, 3, 4...etc) is really just the generation.
 
nice guid there Dave :D

now i got confused at first !! sry for being abit nooby :p

anyhow i just wanna make sure of something !

so for example my FSB is 150 and i overclocked to 250 so i gotta have at least 500 DDR rams to run properly ! and as for quad pumping ! so if i overclocked to 250 the computer reads it as 1000 , correct ?

so its basicly balancing ur rams to overclock properly ur cpu ! :D

if im correct ! its actuely pretty easy :rolleyes:

thanks mate :worship:
 
Yep.

Most CPUs use 266mhz FSB.

So you need at least ddr2-533 aka PC2-4200.

So actual FSB will be 1066mhz and actual ddr will be 533mhz. Bandwidth runs out when both are 1066mhz.
 
name='Hatman' said:
Yep.

Most CPUs use 266mhz FSB.

So you need at least ddr2-533 aka PC2-4200.

So actual FSB will be 1066mhz and actual ddr will be 533mhz. Bandwidth runs out when both are 1066mhz.
Click to expand...

Im glad u made it clear for me Hatman ! :worship:

apreciate the fast responce :D
 
There's 3 determining factors in DDR2, two of which are directly linked and are therefore only one is normally referred too.

Firstly, as you've identified, is the CPU FSB. Second is the memory bus speed and thirdly is the memory speed.

The latter two are linked. DDR2 sends 4 packets at once down the bus. So the memory speed is 1/4 of the bus speed. And to market ram, maufs quote the bus speed as the speed of the ram.

In a 1:1 scenario, using a 266fsb chip (btw hat, 266 is by no means majority. that's just the older conroe chips and a few quads) as an example. The CPU fsb is set to, obviously, 266. To get a true 1:1, the memory bus speed needs to be 4x this, 1066. which as a result of the ram will be running at 266mhz also. So you will need DDR2 -1066 to run a true 1:1 aka PC 8500.
 
name='Hatman' said:
Thanks!

Have nothing 2 do atm lol
Click to expand...

lol ..... :p

name='Ham' said:
There's 3 determining factors in DDR2, two of which are directly linked and are therefore only one is normally referred too.

Firstly, as you've identified, is the CPU FSB. Second is the memory bus speed and thirdly is the memory speed.

The latter two are linked. DDR2 sends 4 packets at once down the bus. So the memory speed is 1/4 of the bus speed. And to market ram, maufs quote the bus speed as the speed of the ram.

In a 1:1 scenario, using a 266fsb chip (btw hat, 266 is by no means majority. that's just the older conroe chips and a few quads) as an example. The CPU fsb is set to, obviously, 266. To get a true 1:1, the memory bus speed needs to be 4x this, 1066. which as a result of the ram will be running at 266mhz also. So you will need DDR2 -1066 to run a true 1:1 aka PC 8500.
Click to expand...

before the 1:1 i understood nothing man !! im sry dont even bother and explain more just give me some time to push everything i learned inside :p lol

anyhow i got the:p main idea :D

thanks mate :worship:
 
name='Ham' said:
In a 1:1 scenario, using a 266fsb chip (btw hat, 266 is by no means majority. that's just the older conroe chips and a few quads) as an example. The CPU fsb is set to, obviously, 266. To get a true 1:1, the memory bus speed needs to be 4x this, 1066. which as a result of the ram will be running at 266mhz also. So you will need DDR2 -1066 to run a true 1:1 aka PC 8500.
Click to expand...

I was under the impression that DDR was simply Double Data Rate, and that for the FSB and RAM to be in a 1:1 ratio where the FSB was 266, the RAM would be 533. I understand that on current intel CPUs the FSB is quad-pumped, so that 1066 RAM would be on a 1:1 ratio with the quad pumped bus-speed, but surely in the BIOS it would have to be on a divider to run at those speeds? What I mean is, I thought the true 1:1 was the slower bus speed, not the quad pumped one? :S
 
Would i be right in thinking then that DDR31600 would be ideal for running a QX6850/790i at 400Mhz bus speed? (1600mhz rated). Sorry if its a dumb question but i'm a bit of a noob when it comes to this and i'm just away to order up a new rig and want to make sure i've made the right component choice......
 
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