Can I install CPU with FSB higher than motherboard's FSB?


My question: Can I install CPU with FSB higher than motherboard’s FSB?

I have a 2-year old motherboard ASUS P4SE/U2 with Celeron 1.7GHz on it and I wanna upgrade to Pentium 4. The manual says the board can support up to 3.06+ GHz Pentium 4/Celeron Northwood/Willamette with FSB 400MHz. But the hightest speed CPUs listed on for this motherboard are:

P4-2.20 GHz (400 FSB, L2 cache:512KB)
P4-2.40 GHz (400 FSB, L2 cache:512KB)
P4-2.50 GHz (400 FSB, L2 cache:512KB)
P4-2.60 GHz (400 FSB, L2 cache:512KB)

I don’t know why they don’t list CPUs between 2.6GHz to 3.06GHz.

Problem is I can’t find any of those to buy. Guess they’re too old. Here is what I can find:

  1. 2.4GHz (533MHz) Prescott 1MB cache
  2. 2.8GHz (533MHz) Prescott 1MB cache
  3. 2.8GHz (800MHz) Prescott 1MB cache
  4. 2.8GHz (533MHz) Northwood 512K cache
  5. 2.8GHz (800MHz) Northwood 512K cache

Would any of these work with my motherboard? I’m interested in #3. I wouldn’t mind having 800MHz FSB CPU running at 400MHz as long as it works and I can benefit from the 1MB cache.

I don’t want to upgrade the motherboard yet unless absolutely necessary. We don’t have to upgrade motherboard everytime we upgrade CPU, do we?

Thanks in advance for any advice.

Well… yes, you can plug in CPUs that are designed to run at higher busspeeds without a problem. However, if you mainboard does not support FSBs over 100Mhz (= 400Mhz because of the quad pumped bus), your CPU will be running at a lower speed, as the multiplier can’t be set!

If you can’t set your FSB to 133 or 200Mhz, you may want to look into overclocking your FSB. If you can set the PCI/AGP divider to 1/4 (for 533) or 1/6 (for 800), you possibly could overclock the CPU FSB and still benefit from the higher FSB without running into problems. There’s no garantuee here, but I’ve seen it working on quite some older systems. It just depens on what your board can do.

BTW… if you can’t find a fitting 3.0 Ghz CPU, why not get an 2.6Ghz CPU? It’s not that fast as the 3Ghz model, but it still beats the crap out of the Cellie :slight_smile:

According to the information on the site your motherboard supports

Celeron 2.8 GHz (400 FSB, L2 cache:128KB) ALL w/1010.001 BIOS upgrade or
P4-2.60 GHz (400 FSB, L2 cache:512KB) ALL .

According to the specs here…

the board supports Socket 478 for Intel Pentium 4 up to 3.06GHz.

Here is what I can find…

Intel Celeron (Pentium 4 Based) 2.8 GHz 400MHz FSB, 128K Cache - Retail

Intel Pentium 4/ 2.8 GHz 400MHz FSB, 512K Cache Processor - OEM (Heatsink and Fan required).

Based on what the specs read above, I’d look for a 400MHz FSB P4, and skip the higher-end 533 chips unless you want a new mainboard. I think you’ll find the cache differences alone between the Celeron and the P4 make a HUGE jump in performance. The early P4 Celerons were poor performers; the long pipelines of the P4 core require decent size caches to keep the pipes full with instructions. The P4 class Celerons suffered greatly due to their smaller caches, which resulted in more idle time waiting for instructions, and more cache misses. I’d bet that a P4 at 2.6 or 2.8GHz would make you feel like you have a new machine.

Running a CPU rated higher than 400MHz FSB will not only run the CPU slower than rated spec, but may also cause additional issues (your mainboard may not support Hyperthreaded CPU’s). As for why your mainboard doesn’t list newer CPU’sas compatible, you answered your own question: It doesn’t support a 533MHz front side bus.

Thanks, that’s good news if I can really do that. Except that LoneWolf15 says something different.

As I mentioned in the first post, I’m interested in #3. 2.8GHz (800MHz) Prescott 1MB cache. #2-#5 all have similar prices while #1 is £30 cheaper.

Thanks, that’s what I already checked and posted in the original post.

I’m in the UK and it’s easier (and may also be cheaper) to find the CPUs #1-#5 listed in the original post.

I do not want a new motherboard.

Exactly! It takes 10 hours to convert a DVD to XviD with this Celeron 1.7GHz and people says it should only takes 2 hours with Pentium 4!

Now, what you say here is different from what Dee-ehn says.

  1. You say that it could cause additional issues. Could you give some examples? Surely not supporting hyperthreading is not an “issue” as long as the CPU can run fine (this leads the the next question).
  2. When you say CPU X is not support by motherboard Y, do you mean a) CPU X wouldn’t run at all OR b) CPU X would run but at the max speed supported by the motherboard Y? My understanding was that it’s (b) and Dee-ehn confirmed that it’s (b) but from your reply I gathered you mean (a).

Similarly, the reason the newer CPUs are not listed could be because they are not “fully” supported i.e., not all features are supported (based on Dee-ehn’s reply). Or maybe because they wouldn’t run at all (based on your reply).

Dee-ehn, LoneWolf15: could you confirm please?

If #3. 2.8GHz (800MHz) Prescott 1MB cache can run fine (as best as the motherboard can support) without a problem I won’t upgrade the motherboard.

As far as I know (mostly from my own experiences), these P4 CPUs will work on older boards just fine, as long as the settings are correct (powersettings). They will work on lower speeds and without HT enabled of course.

Recently I put a 2.8 Ghz Northwood with HT on an old i845 based board (with SDR memory) and it ran fine. Overclocked the FSB and it worked like a charm!

If you want to be really sure (as there’s no 100% garantuee), you might want to take your computer to a store and have it tried there. Find a good store btw… or else they’ll be selling you a new mainboard as well :wink:

Prescott uses a different voltage, so I’d be wary of putting ANY Prescott core cip on a board that doesnt explicitly support it.

Best chance, out of those you list, would be #4 - The 2.8 GHz northwood 533 - which if you cannot overclock the FSB at all, would run at 2.1 GHz - the 800 FSB models would run at half speed, if they run at all
I guess you’re not looking for more Celeron power!

Ebay is a risky place to get CPU’s, but it may be your last resort Only a 1.8, but it has the 512k cache

Quite a few 1.8’s around on ebay, if you think the bigger cahce will make more difference than a faster Celery

I’d go with LoveWolf and Matth, you can’t run all CPUs on your mainboard for reasons mentioned earlier in the thread.

Thanks all. I’ve checked the BIOS settings.

CPU Speed: [Manual|1700MHz|2266MHz]
CPU Frequency Multiple: 17x <- (always fixed)
CPU External Frequency: [100/33|101/34|102/34|…|133/33|134/34|…|166/33]
Memory Frequency: [Auto|200MHz|266MHz|333MHz|400MHz]
CPU Vcore Set: Auto
CPU Vcore: [1.850V|1.825V|1.800V|1.775V|1.750V]

Underscored means current settings. Current CPU is 1.7GHz Celeron. I don’t know why there are only 1.7GHz and 2.266GHz there but if I change it to 2.266GHz the CPU External Frequency will change to 133/33 while other settings remain the unchanged.

Would the mainboard accept “#4. 2.8GHz (533MHz) Northwood 512K” or any of the Prescott models (tempted by 1MB cache)? I don’t quite understand those many 1xx/3x External Frequency options and why there is only fixed 17x for Frequency Multiple though.


Intel Multipliers have been hard-locked since the last days of the Pentium 1 and MMX.
AMD spat on their enthusiast base, when they too implemented ever more vicious locking.

the 1.7GHz Celeron runs at a Multiplier of 17x 100 clock - with dual DDR for a quad-pumped 400 FSB

The fact it offers 2266MHz (17x 133.3)
Suggests that you could use, at least unofficially, a 533 FSB processor.
Not sure if a Celeron can be expected to overclock to that level, and not sure if the chipset will - I’ve seen boards that offer values in bios that are well beyond the chipset’s stability limits.

I’d be very reluctant to put a Prescott on a motherboard that doesn’t explicitly support it though, but the 2.8GHz 533 FSB Northwood looks possible, if the motherboard will hold the chipset overclock (unless they updated the chipset - that happens).

Even if his Celeron does make it up to an overclocked speed, the lack of cache hurts even more as clock speed rises, making the Celeron a poor choice for overclocking.

I’d say this is his best bet:

I have read your posting 'bout FSB.

I have the some problem but my board is 800 with CeleronD 331. 800 too.
Now, I want to put the C2D 8400 1333.

How’s your idea 'bout that.
Can that couple running? Although with lower FSB…

My email is

and My FB is: iwen daffa nina with that email.

[[B]edit by Dee[/B]]
Removed email address.

Why ressurect this more than EIGHT YEAR OLD topic from the dead?

Suwendra, if you have a question abut upgrading an older Mother Board UP to a Core 2 Duo E8400 why not start a discussion as a new topic?

Many newer boards actually made for the 1333MHZ fsb and 1066MHz FSB CPU’s
were “Back compatible” to Socket 775 Pentium 4 CPU’s with 800MHz FSB
as well as their “Celeron” versions.

Having detailed information about your MoBo would let us know.