P4B in a P4A board

Mitch007 · Sep 1, 2004

From sig below, I have a 2.4Gig P4, and manully tweaked FSB multiplier to get to 2.8Gig. (In bios FSB = 116!) But to do this I've also had to drop the mem clock ratio, since board won't go above 333Mhz ram for some reason (although. as you can see I have PC3200 to get aggressive timing).

Can I drop in a 2.8Gig P4B (or higher) with FSB 533, and manually set FSB to 133 to get to the 2.8Gig. this will allow me to get to 333Mhz memory clock.

I can get a processor real cheap, so no MoBo upgrades needed, or even wanted, since I have a really stable machine (but want more mem bandwidth).

I know board won't auto detect and set 533, it's not supported.

MIS645Ultra/P42.4@2.8Gig/2*Corsair 256MBit CL2-2-2-7XMSLLPT PC3200 DDR RAM/450W Enermax PSU/1*40Gig 7200rpm Wes-Dig/1*20Gig 7200 Hitachi Disk/GeF4 Ti4200 XFX Turbo 670/250 Ram/Core MHz.

xeenrecoil · Sep 1, 2004

heya Mitch;

The answer is, hell no dont try it you will damage the motherboard. The 400FSB chipset uses a different multiplier ratio, if you try and stick a 533FSB CPU you will be trying to run a frequency not supported by the chipset way beyond its nominal range, and in effect overclock the chipset to the point it says the hell with you, now worst case is it will destabalize permanently, but no one wants a motherboard that they cant use.

I tried the exact same thing you want to try with an Asus P4G8X-D, i put a p4c 3Ghz on a native 166Mhz FSB chipset, well as you can imagine the chipset made a high pitched noise for about 30 seconds and never worked right again. So the answer is a definate no. If you want to get a new CPU with a faster FSB you might as well get the p4c 3Ghz, and you will also need to get a new Mobo, look for the Abit IS7, it is a very very good inexpensive mobo, you can get one for $75 USD.

Mitch007 · Sep 1, 2004

I thought the multiplier ratio was set by the CPU, and is on the CPU, so if I manually adjust the FSB from 100Mhz to 133 if I switch from a 400FSB to 533FSB 2.8GP4, i thought i'd be ok, and may be able to overclock even further.....

MIS645Ultra/P42.4@2.8Gig/2*Corsair 256MBit CL2-2-2-7XMSLLPT PC3200 DDR RAM/450W Enermax PSU/1*40Gig 7200rpm Wes-Dig/1*20Gig 7200 Hitachi Disk/GeF4 Ti4200 XFX Turbo 670/250 Ram/Core MHz.

xeenrecoil · Sep 1, 2004

heya Mitch:

This is Intel not a AMD, the CPU multiplier is locked, and always has been, which means you will be trying to run the external FSB at 133, on a chipset that is native 100, it just wont work, i said i tried it, and with a much better and much more expensive motherboard then what you have, trust me it wont work. What ever your multilier is now, lets say its 24 , and your FSB is 100 that would be 24x100@2400Mhz, now what happens is the chipset is native 100Mhz you are trying to run a native 133Mhz FSB processor on a native 100Mhz FSB, if you do the math you will see it just wont work the chipset is only capable of multiplying at 100x[Static CPU Multiplier] reguardless if you soft OC it or not. The internal bus has to match the external bus, and does its math based on that, the math comes out all wrong and the Chipset frequency goes way the hell out of nominal range. If you want to try it be my guest, i tried it and lost a $230 mobo because of it, but maybe you dont care about the mobo, if you dont care about it then go for it...but dont say i didnt warn you.

xeenrecoil · Sep 1, 2004

heya Mitch:

Here is the math incase you wanted it, the formula i am going to be basing this off of is native 533Mhz FSB chipset with a p4b 2.4Ghz 533FSb with a x18 multiplier, versus a p4c 2.4Ghz 800FSB with a x12 multiplier.

Now what happens is the chipset will revert back to using a 100Mhz FSB formula reguardless of what what you soft clock the external FSB to, so basically you are trying to use a internal frequency of 100Mhz and an external frequency of 200Mhz, on AUTO the chipset sees this and does the math accordingly and sets the cpu speed at 1200Mhz, If you try and set it manually it comes out to 100x8 instead of 200x4, and it simply wont work.

In your case the chipset will use the equasion 66x8 for the external frequency instead of 133x4, see what im getting at here?

Mitch007 · Sep 1, 2004

I get you now, the multiplier on the chip affects more than just CPU

MIS645Ultra/P42.4@2.8Gig/2*Corsair 256MBit CL2-2-2-7XMSLLPT PC3200 DDR RAM/450W Enermax PSU/1*40Gig 7200rpm Wes-Dig/1*20Gig 7200 Hitachi Disk/GeF4 Ti4200 XFX Turbo 670/250 Ram/Core MHz.

Crashman · Sep 2, 2004

The 645 actually supports 133MHz FSB. In fact all the old 100MHz (400 bus) chipsets could be overclocked past 133 to the best of my knowledge. So I would definatly try that.

A lot of guys used to flash the old Asus P4S333 with P4S533 BIOS to get the full functionality of 133MHz FSB (533 bus) detection and reported 0 problems.

You'll probably have to set the memory at DDR333 though. Perhaps even DDR266, which is synchronous but sucks because single channel provides only 1/2 the bandwidth the CPU wants.

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Crashman · Sep 2, 2004

Nah, I've never seen a 400 bus board that wouldn't do 133MHz FSB.

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Mitch007 · Sep 2, 2004

You think it's worth a pop then?

I can not go higher than 116FSB, but think it's the CPU packing in (I hope) since the P4's a later model and is probably tighter screen at manufaccture.
I have already backed off the mem to get the over clock on the P4 2.4, so no issue, and I guess the extra B/W to memory with a 533 will help loads?

MIS645Ultra/P42.4@2.8Gig/2*Corsair 256MBit CL2-2-2-7XMSLLPT PC3200 DDR RAM/450W Enermax PSU/1*40Gig 7200rpm Wes-Dig/1*20Gig 7200 Hitachi Disk/GeF4 Ti4200 XFX Turbo 670/250 Ram/Core MHz.

Crashman · Sep 2, 2004

Nope, I don't think it's worth it. The only thing that's going to make your PC noticably faster is getting a noticably faster CPU. The higher bus speed will still be choaked by the relatively low bandwidth of the memory.

Only a place as big as the internet could be home to a hero as big as Crashman!
Only a place as big as the internet could be home to an ego as large as Crashman's!

xeenrecoil · Sep 2, 2004

Crashman;

Go stick a 800FSB p4c on a native 533FSB chipset and see what happens, the math isnt suported and it wont run properly reguardless of what you soft clock the FSB to. The problem lies in the multiplier, since the CPU multiplier is locked it will not be the proper multiplier at the higher FSB speed, as the math for the native 533FSB and native 800FSB are different, the chipset is coded to support a Native maximum of 533FSB and has no math for Native 800FSB, if you think about it the math just doesnt work, so the chipset falls back to the next slowest compatable bus speed.

jammydodger · Sep 2, 2004

Going from a P4b to a P4c raises the FSB from 133Mhz (533 = 133*4) to 200Mhz (800Mhz = 200*4) this is a 44% increase in FSB.
However going from a P4a to a P4b is only a 33% increase which is why a board supporting a P4a will be more likly to support a P4b, than a board that supports a P4b will be to support a P4c.

I still think the whole idea is pointless though because you are investing all this money to get 17% increase in memory bandwidth which will probably transform into a 8% increase in real world performance.

Crashman · Sep 3, 2004

Using a P4B in a P4A board is a totally different game. The P4 2.4B is identicle in every way to the P4 1.8A except for the bus speed detection pin assignments.

Some boards have problems with HT enabled processors, but I don't think he mentioned the 3.06.

Anyway, I told him in another thread that it should work but was a waste of money because his single channel memory bus is the bottleneck now.

Only a place as big as the internet could be home to a hero as big as Crashman!
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endyen · Sep 3, 2004

Sometimes you can even run a P4c, in a P4b boared, like <A HREF="http://www.tomshardware.com/motherboard/20030429/index.html" target="_new">http://www.tomshardware.com/motherboard/20030429/index.html</A>

Crashman · Sep 3, 2004

True, but rare.

Only a place as big as the internet could be home to a hero as big as Crashman!
Only a place as big as the internet could be home to an ego as large as Crashman's!

Mitch007 · Sep 3, 2004

Dropping my CPU/MEM ration and lifting my FSB to 116 on std 400FSB P4A gave me a significant performance increase, which I believe is due to the increase in meme B/W or bandwith between CPU and MEM to be more precise, and hence my thoughts on dropping in a 522FSB P4B, with 133 FSB I can get a P4B2.8G running at 2.8 and have my PC3200 running back at 333Mhz (fastest this board will support)

at 2.4Gig stock speed, my mem will run at 333Mhz, I initially had PC2700 in the board, but thought this was limiting overclock, so I got 3200. But still no joy, so I dropped mem cpu ratio and was able to lift FSB to get P42.4 running at 2.8Gig.....

MIS645Ultra/P42.4@2.8Gig/2*Corsair 256MBit CL2-2-2-7XMSLLPT PC3200 DDR RAM/450W Enermax PSU/1*40Gig 7200rpm Wes-Dig/1*20Gig 7200 Hitachi Disk/GeF4 Ti4200 XFX Turbo 670/250 Ram/Core MHz.

jammydodger · Sep 3, 2004

The reason you got a performance boost was because the CPU was going from 2.4Ghz to 2.8Ghz. If you get a P4b running at 2.8Ghz there will be no speed difference between that and your overclocked 2.4@2.8

Crashman · Sep 3, 2004

When you overclock, you overclock everything. Say you had your CPU originally set for 400 bus (100MHz clock) and your RAM set for DDR333 (166MHz clock). Then you overclocked your FSB by 16% to 116MHz clock. Your RAM will also increase by 16% to 193MHz (DDR386). Your increase comes from both the CPU and RAM running faster.

So your RAM isn't running at 333. It can't be. If you have it set to run at 333, it's running 384. If you had it set to run 266, it would be running 309. Because it's running 16% faster than what you set it as.

If you raise your CPU bus to 133, BIOS will probably be smart enough to drop the RAM ratio from CPU:RAM of 100:166 (a 3:5 ratio) to 133:166 (a 4:5 ratio). That's because these ratios are supported by your chipset. And the drop in ratio would put your memory back at 333, instead of 384 like it is now. So you might actually loose performance by going to the 2.8B.

Only a place as big as the internet could be home to a hero as big as Crashman!
Only a place as big as the internet could be home to an ego as large as Crashman's!

P4B in a P4A board

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