FSB and rated FSB query

[CurlyWhirly]

My old PC was around 6 years old and it only had a FSB of 333 Mhz (2x166 Mhz DDR) and, as I understand it, data flowed between the CPU and memory at this speed.

I'm now running a Q9650 (below)

This is a lot more complex than before as the memory itself runs at 800 Mhz (2x400 Mhz DDR) but the FSB runs at 333 Mhz and yet the rated FSB runs at 1333 Mhz

What speed would the data actually run at between CPU and memory?

I guess it's 1333 Mhz (rated FSB) in which case what's the point of the FSB speed of 333 Mhz

Sorry if it's a noob question

 

[95thrifles]

The actual FSB is 333, however this is quad pumped to give you your rated FSB of 1333

 

[CurlyWhirly]

The actual FSB is 333, however this is quad pumped to give you your rated FSB of 1333

Thank you

I just googled quad pumping but am at a loss to understand why the rated FSB isn't 4x400 Mhz=1600 Mhz (which is the speed of the actual memory itself) rather than 1333 Mhz.

It must be a limitation of either the mobo or chipset as the QX9770 manages it.

 

[silvercut]

Then you RAM is probably running at 667Mhz (i.e 333mhz) and not 800Mhz, post the memory tab of CPU-Z ...

 

[Jokester]

You can run RAM out of sync with your CPU on LGA775.

 

[CurlyWhirly]

Then you RAM is probably running at 667Mhz (i.e 333mhz) and not 800Mhz, post the memory tab of CPU-Z ...

 

[CurlyWhirly]

You can run RAM out of sync with your CPU on LGA775.

Is there any advantage or disadvantage in doing this

 

[AgedIdiot]

Is there any advantage or disadvantage in doing this

Disadvantage Not really - if any only small.

AND it helps you in overclocking your cpu by not tying 1:1 the fsb and the ram.

It's being used in your cpu-z picture but , if I interpret correctly, not to slow down your ram to the fsb speed (333) but to increase it to its own speed


Your RAM is running per cpu-z @ 800mhz (to be precise 799.4 calculated by DRAM frequency x2)

The FSB/DRAM entry shows the realationship between the FSB and the ram speed i.e 5:6 (divide the FSB (333) by 5 and then multiply by 6). Your motherboard may have set this for you

My simplistic way of explaining which I hope assists.

 

[Topitoff]

Is there any advantage or disadvantage in doing this

For benchmarking Yes it's an advantage; but in the real world performance -not really - as above^.

You gain because of the extra speed of the RAM, you lose as it's out of sync with the cpu and a lot of times has to wait for the cpu.

The best way to make the most of the RAM is run it in sync but reduce the multi of the cpu and increase the FSB; ie a 2.4GHz CPU system will run faster if it has a multi of 6 and FSB of 400, than a multi of 12 and FSB of 200.

Hope this helps

 

[AgedIdiot]

Hope this helps

Not sure if it helped the OP but it did me ( I now know why 1:1 IS better)- My Thanks !!

 

[CurlyWhirly]

Disadvantage Not really - if any only small.

AND it helps you in overclocking your cpu by not tying 1:1 the fsb and the ram.

It's being used in your cpu-z picture but , if I interpret correctly, not to slow down your ram to the fsb speed (333) but to increase it to its own speed


Your RAM is running per cpu-z @ 800mhz (to be precise 799.4 calculated by DRAM frequency x2)

The FSB/DRAM entry shows the relationship between the FSB and the ram speed i.e 5:6 (divide the FSB (333) by 5 and then multiply by 6). Your motherboard may have set this for you

My simplistic way of explaining which I hope assists.

Yes thanks for the above explanation also to Topitoff

There's a lot more involved to RAM and FSB as was the case with Socket A CPU's


One final query if I may, would overclocking my CPU affect the speed of the PCI bus (not PCI Express) as I have a Creative X-fi sound card plugged into it and with my old system (Socket A mobo), overclocking my CPU used to cause crackling with the speakers as I think that the PCI bus speed was increased above tolerance levels

 

[AgedIdiot]

Would not expect it to.

Just check your motherboard manual to be sure.