I'm really confused about FSB....

[gopunk]

okay on newegg, they say that FSB for the Abit IC7-G is 800 mhz... but then in anandtech's review of that board, they list it as 412 mhz. why the discrepancy?

also, newegg says the ic-7 can take dual ddr ram up to 400mhz. does this mean it's up to 800? will it run pc3700? because i was reading ocz tech's faq, and they said the FSB must be able to reach 466 mhz.... and said that most newer boards can take it. the only way i can make these two statements fit is if i take "dual" to mean multiply 400 by 2...

ah it's so confusing....

thanks

 

[Schadenfroh]

your looking at the wrong number, the frontside bus of the abit is 800mhz, as long as you have a p4 with a C in it. you pair that with 400mhz ram. in theory wouldnt 400mhz Dual Channel DDR = match for 800mhz fsb?

 

[gopunk]

Originally posted by: Schadenfroh
your looking at the wrong number, the frontside bus of the abit is 800mhz, as long as you have a p4 with a C in it. you pair that with 400mhz ram. in theory wouldnt 400mhz Dual Channel DDR = match for 800mhz fsb?

well i dunno, i guess so?

so does that mean the board can't handle the pc3700 ram? because i don't see anyboards with fsb potentially greater than 800..... or is it that the 466 ocz mentioned is already multiplied by 2... so it's actually 233 mhz....

and why do newegg and anandtech differ?

 

[iuvas]

It's all based of an actual 200 mhz FSB.

The proc says 800mhz because it's "Quad-pumped" and you are correct about the memory, as its DDR so 2x 200=400

 

[Lonyo]

The PC3700 ram can run at a lower speed.
RAM is rated at its highest confirmed speed, not its only speed. And you can always OC your P4

 

[gopunk]

Originally posted by: iuvas
It's all based of an actual 200 mhz FSB.

The proc says 800mhz because it's "Quad-pumped" and you are correct about the memory, as its DDR so 2x 200=400

oh.... ok, thanks so let me just make sure i have things clear... when it says 800 mhz, it can take ram up to 800 mhz, which is actually ddr 400 mhz? so the pc3700 that is 466mhz is actually ddr 233 mhz? how do they get the 3700? i used to know that... heh.

 

[gopunk]

Originally posted by: Lonyo
The PC3700 ram can run at a lower speed.
RAM is rated at its highest confirmed speed, not its only speed. And you can always OC your P4

yea haha, but i feel unfulfilled if i'm buying ram and not getting full fsb out of it

 

[Lonyo]

P4 800MHz quad pumped bus = 200MHz FSB x 4 to give 800Hz effective.

PC3700 = 3700MB/s max theoretical throughput.
Divide by 8 (8 bits in a byte) we get 462(MHz) actual speed, or 233 or so real speed (233x2 gives the 462 since it's DDr (Double data rate, x2))

You would probably be able to overclock the P4 to 233MHz FSB, so you would be using it to its full potential, or you could try the RAM at 250MHz (if it will overclock) by runing the RAM out of sync with the FSB using a 4:5 divider (200MHz FSB:250MHz RAM (500MHz DDR)

You should probably get faster rated RAM anyway, as then you will probably be able to run tighter latency timings at the processors speed (200MHz).

RAM's max rated speed is 233MHz, CPU runs at 200MHz, these numbers are multiplied to give the other numbers, but those are the basic numbers.

 

[DaveSimmons]

If you aren't overclocking, all you need is:
- the i865 or i875 board of your choice (AT favorites are the IS7 and Asus P4P800 deluxe, since they run just as fast as the IC7 and P4C.)
- P4 C of your choice.
- 2 same-size sticks of PC3200 DDR. The "CL" value makes a small difference, CL=3 is 2-3% slower than CL=2.5, which is also a little slower than the hideously overpriced CL=2. (ed Crucial sells CL3 and mushkin sells 2.5 at decent prices)

The 412 MHz in AT's review was a 3% overclock, 400 MHz (200x2) is the stock DDR speed and 800 MHz (200x4) is the stock P4 FSB speed.

The last confusing bit is that for heavy overlocks you can either run the memory at a 1:1 ratio with the processor ( (200+N) x2 and (200+N) x4) which needs ultra-fast PC3500/700/4000 -or- set the ratio at 5:4 so when you OC a P4 2.4C to 3.0C (by raising the P4 FSB to 250 x 4 = 1000) the memory is still only running at 200 x 2 and you only need PC3200.

 

[salvorhardin]

I hope I can clarify A few things, the spec on the board means that it can use 800MHz fsb P4s, newer P4 with a C stepping have the 800MHz fsb which is really running at 200MHz but is the quad pumped to run at 800MHz. On memory the numbers after the pc???? are the maximum transfer rate for that memory, for example PC3700 has a maximum rated bandwidth of 3,700 MB/s, which when converted to MHz is 466MHz that in reality is 233MHz double pumped. I believe that Intels 875 chipset is capable of dual channel so if you put two sticks of PC3200 ram it should match the bandwidth needs of the fsb. People use the PC3700 ram mainly when they want to overclock their fsb on the P4. I hope I didn't confuse you more, this is how I inderstand it and if i'm wrong i'm sure someone will reply with the correct answer.

should have typed faster

 

[gopunk]

Originally posted by: Lonyo
P4 800MHz quad pumped bus = 200MHz FSB x 4 to give 800Hz effective.

PC3700 = 3700MB/s max theoretical throughput.
Divide by 8 (8 bits in a byte) we get 462(MHz) actual speed, or 233 or so real speed (233x2 gives the 462 since it's DDr (Double data rate, x2))

You would probably be able to overclock the P4 to 233MHz FSB, so you would be using it to its full potential, or you could try the RAM at 250MHz (if it will overclock) by runing the RAM out of sync with the FSB using a 4:5 divider (200MHz FSB:250MHz RAM (500MHz DDR)

You should probably get faster rated RAM anyway, as then you will probably be able to run tighter latency timings at the processors speed (200MHz).

RAM's max rated speed is 233MHz, CPU runs at 200MHz, these numbers are multiplied to give the other numbers, but those are the basic numbers.

oh i see... so we compare the 233 mhz and the 200 mhz.... but why do we do this, if the actual speed of the ram is 462 and the effective speed of the bus is 800?

to overclock, do i just go in a change the bios settings? i remember a few years ago people were talking about using pencils and connecting some stuff on the cpu or some crazy stuff like that.... i don't seem to be reading much about that this time around

 

[Lonyo]

Pencils and stuff was to change the bridges so you could unlock the CPU multiplier (number that multiplied the FSB to give CPU frequency) but P4's can't be unlocked.
The way to overclock a P4 is to go into the BIOS and up the FSB frequency. Simple as that, really. Sometimes you have to increase the voltage to the CPU too to give it more power if its unstable.
This is where having RAM that runs with a base speed of 233MHz helps, because then you shoul deasily be able to overclock the CPU FSB to 233MHz.
You don't need pencils anmore though, thankfully, and the only way to overclock the P4 is through increasing the FSB.

 

[gopunk]

Originally posted by: salvorhardin
I hope I can clarify A few things, the spec on the board means that it can use 800MHz fsb P4s, newer P4 with a C stepping have the 800MHz fsb which is really running at 200MHz but is the quad pumped to run at 800MHz. On memory the numbers after the pc???? are the maximum transfer rate for that memory, for example PC3700 has a maximum rated bandwidth of 3,700 MB/s, which when converted to MHz is 466MHz that in reality is 233MHz double pumped. I believe that Intels 875 chipset is capable of dual channel so if you put two sticks of PC3200 ram it should match the bandwidth needs of the fsb. People use the PC3700 ram mainly when they want to overclock their fsb on the P4. I hope I didn't confuse you more, this is how I inderstand it and if i'm wrong i'm sure someone will reply with the correct answer.

should have typed faster

thanks for the info so dual channel means that we multiply the speed of the ram yet again? so pc3200 would then have an effective speed of 800 mhz? so everything should be perfect then... ?

 

[DaveSimmons]

to overclock, do i just go in a change the bios settings? i remember a few years ago people were talking about using pencils and connecting some stuff on the cpu or some crazy stuff like that.... i don't seem to be reading much about that this time around

No pencils -- the P4 is multiplier-locked (e.g. 2.4 = 12 x 200) but are not FSB locked (so the same P4 2.4C at 12 x 250 x 200 = 3.0 GHz).

You just go into the BIOS and up the FSB, and (depending on memory speed) either keep the memory ration at 1:1 or lower it to 5:4.

 

[salvorhardin]

dual channel means you will have twice the bandwidth, with two sticks of pc3200 the fsb theoretically can transfer information to and from the memory at 6,400MB/s exactly matching the bandwidth size of the fsb.

 

[gopunk]

Originally posted by: DaveSimmons
If you aren't overclocking, all you need is:
- the i865 or i875 board of your choice (AT favorites are the IS7 and Asus P4P800 deluxe, since they run just as fast as the IC7 and P4C.)
- P4 C of your choice.
- 2 same-size sticks of PC3200 DDR. The "CL" value makes a small difference, CL=3 is 2-3% slower than CL=2.5, which is also a little slower than the hideously overpriced CL=2. (ed Crucial sells CL3 and mushkin sells 2.5 at decent prices)

The 412 MHz in AT's review was a 3% overclock, 400 MHz (200x2) is the stock DDR speed and 800 MHz (200x4) is the stock P4 FSB speed.

The last confusing bit is that for heavy overlocks you can either run the memory at a 1:1 ratio with the processor ( (200+N) x2 and (200+N) x4) which needs ultra-fast PC3500/700/4000 -or- set the ratio at 5:4 so when you OC a P4 2.4C to 3.0C (by raising the P4 FSB to 250 x 4 = 1000) the memory is still only running at 200 x 2 and you only need PC3200.

ahh... that clears up things.... so for these heavy overclocks... do i need to get a pricy fan/hs and use AC, or am I fine with the retail fan/hs included with the processor?

 

[DaveSimmons]

ahh... that clears up things.... so for these heavy overclocks... do i need to get a pricy fan/hs and use AC, or am I fine with the retail fan/hs included with the processor?

Most people seem to be reaching 3.0 GHz with a 2.4C at 250 FSB and just the retail HSF. The super-HSFs are for the people going even higher.

But I'm no expert on OC, I tend to be lazy and spend the extra $$$ to run at stock speed.

(ed) and be sure to look at the total price of OC vs. non-OC if you spend an extra $200 buying ultra-fast RAM instead of running at 5:4 or just buying a faster P4.

 

[gopunk]

Originally posted by: salvorhardin
dual channel means you will have twice the bandwidth, with two sticks of pc3200 the fsb theoretically can transfer information to and from the memory at 6,400MB/s exactly matching the bandwidth size of the fsb.

ok sounds perfect!

so we have:

fsb:
200 mhz, quad pumped to 800 mhz

memory:
pc3200 which means 200 actual, 400 effective, but then the mb supports dual channel, so it's actually 800 effective

so if i wanted to overclock, the simplest way (ie, without the 5:4 stuff) would be simply to go into the bios, change the fsb to 233 mhz actual, then get pc3700 ram.

hurrah! i understand, thanks everyone

 

[snailophone]

so basically, if you had an abit is-7 motherboard, 2 sticks of DDR400 dual channel RAM, and a 2.4c gig P4 CPU you would be taking full advantage of the FSB??? Am I right on this???