Intel Mobile Pentium 4 M Exploration

Mobile P4M logoThis is pretty much the only thing I feel bad about just getting rid of from my old site so thought the least I could do is just copy it across. It’s a bit outdated but I hope it’s of use to some people. Cheers.

I came across the possibility of using Mobile Intel Pentium 4 Processors – M (to give them the official title) in desktops while sourcing components for the company I worked for. My boss wanted these tiny cube systems to sit looking pretty on the desks of our office. However, he also wanted top of the range performance and didn’t even think about the noise. As a quiet PC enthusiast I said he would need some impressive cooling system if he didn’t want the CPU fan to sound like a jet engine right next to his ear!

So I set about researching and stumbled across a few threads in various forums (huge thanks to the people at Silent PC Review and AnandTech) which explained how I could use these CPU’s in desktops. Although the CPU’s didn’t turn up on eBay often, I got hold of 2, tested them out, got very excited and tried to source more! When the chance came around to buy a large quantity of them I decided to grab them all, put some effort in and resell them. This page is here for the people who want to know more about these great CPU’s, although I no longer have any left for sale I’m afraid.

Mobile P4M waferThe Mobile Intel Pentium 4-M is based on the same Northwood core as it’s desktop equivalent. Indeed they most likely came the same wafer and are essentially identical in design. However, processors destined for mobile use are ‘hand picked’, almost certainly from the middle of the wafer where the silicon is best. They are the cream of the crop, able to match or exceed the performance of their desktop siblings while running at a lower voltage. If you look at it from this point of you, standard desktop Pentium 4’s are the rejects that don’t quite make the grade!

Where the two processors differ is that the mobile P4-M makes use of Enhanced Intel SpeedStep technology, which is designed to reduce the clock speed of the processor when not under heavy use, thus preserving a laptop’s battery. This basically involves reducing the default bus speed multiplier (17 in the case of a 1.7 GHz Mobile P4-M) to 12, resulting in a clock speed of 1.2 GHz. When placed in a desktop motherboard which doesn’t understand SpeedStep technology, the processors run at the default 12 multiplier with a bus speed of 100 MHz (1.2 GHz). I’m unaware of any consumer orientated motherboards with support for SpeedStep.

Now you may think this SpeedStep technology is a bad thing for anyone wanting to use these processors in a desktop. However, by simply increasing the FSB (Front Side Bus) from 100 MHz to 200 MHz the cpu will easily run at 2.4 GHz and benefit from a substantially faster bus speed.

A point worth making is that Mobile Celeron processors don’t feature SpeedStep technology and therefore retain their original clock multiplier. However, with modern motherboards officially supporting an 800MHz FSB (200MHz quad-pumped) and many enthusiast targeted motherboards allowing even greater bus speeds it seems silly to hamper the speed of you system by sticking to the slow, old 100MHz bus speed.

An important physical difference anyone can spot is that the Pentium 4-M doesn’t have a heat spreader. This has a significant impact on reducing core temperatures as the heat has one less layer to dissipate through. This is not only of interest to quiet pc enthusiasts but anyone who likes to keep their CPU’s core cool and healthy.

Gigabyte GA-8I875The rig I’ve set up for testing all the processors I’ve bought is based around a Gigabyte GA-8I875 (Gigabyte are one of the few manufactures to allow VCore undervolting). I picked it up as B-Stock from for a very reasonable price. I’ve got a couple of 256mb sticks of Samsung DDR400 (nothing to write home about) running in dual channel configuration. When I eventually make a proper PC out of this motherboard I will invest in some Kingmax DDR500 😉

Based on the Intel 875P north bridge and ICH5R south bridge, in terms of features the only thing slightly disappointing is that the Gigabit ethernet is connected over the PCI bus instead of via CSA but like I’m ever gonna tell the difference!

Something which I would really have liked to see is the ability to select a 1:1 FSB/RAM ratio even when the CPU doesn’t have a 800 (200 quad-pumped) MHz FSB. This would have allowed a us more flexibility when overclocking, or in this case, bringing the processor back up to stock speed.

The Mobile Pentium 4-M has a 400 (100 quad-pumped) MHz FSB. Therefore it is necessary to do a bit of a modification to the processor in order to fool the motherboard into thinking we’ve inserted a 800 FSB CPU.

The modification is basically breaking the BSEL1 pin from the bottom of the CPU. This is not an easy task; it requires a steady hand, good eyesight even when using a ‘third-hand’ magnifying glass and lots of patience, taking care not to damage any of the surrounding pins.

Once performed successfully the processor will show up as a 2.4 GHz (200 x 12) CPU by default in 800 FSB motherboards, allowing much more flexibility with memory speeds as well as flawless operation in motherboards which don’t offer a manual bus speed selection. Click here for a pin layout of the Mobile Intel Pentium 4-M which shows which pin you need to break off.

Anyway, here are some preliminary testing results of the 1.8GHz Mobile Intel Pentium 4-M Processor (SL6FH). The testing was performed on the bench with an ambient temp of around 20C. The testing is by no means deadly accurate or scientific, just a rough guide. The power supply I used was just a cheap and nasty thing and I’m sure a higher quality PSU would help stability. I used a Thermalright SKU-800 heatsink with a Zalman 92mm fan running at full pelt. This is certainly an overkill at lower speeds but it made testing consistent across the board.

Speed (GHz)BIOS VCore (Volts)Idle Temp (Degrees Centigrade)Prime95 Temp (Degrees Centigrade)Comments
1.200.83752830Will run fanless at 35 when idle!
1.600.83753032Performance increase makes this speed worthwhile over 1.2 GHz
2.260.83753134Fastest speed achievable without increasing the voltage from 0.8375
2.401.33753238An excellent compromise between heat and speed
3.201.68003449I reckon there’s more speed in there too!

As you can see it seems feasible to run this CPU fanless at 1.2 or 1.6 GHz. 15 minutes of Prime95 gradually built the temperature up to 65 but for everyday average use with a very slow fan or good case airflow you could have a very quiet system. I personally would rather run a little faster and reduce the bus speed using ClockGen when not in use (I leave mine on 24/7 usually). Amazingly this CPU will go all the way up to 3 GHz and beyond! I’m not sure but I think those temps are less than the equivalently clocked desktop processor which just shows that even when stretched to the extreme these CPU’s are truely “The Daddy”!

Perhaps someone can help me with this but I suspect the 8I875 does not allow VCore to go all the way down to 0.8375. The diagnostic utilities I used, SpeedFan and CPU-Z, reported it as 1.25v, which I could put down to the voltage being out of the sensors range. However, I seriously doubt I would be able to hit 2.26GHz on such a low voltage. Given that the default VCore when used in a laptop is 1.2/1.3v it seems that Gigabyte have only implemented voltage adjustment to 1.25. Maybe it’s a bug in the BIOS, I’m using the latest version (F8). Someone else’s opinion on this would be most welcome. I’m not sure how I could test for sure.

Soltek SL-865PE-LFinally got a new motherboard, or rather two. One to keep on the bench for testing and one to replace my Gigabyte GA-8I875 as my main computer. I was less than impressed with the Gigabyte’s stubbornness to change the actual VCore despite allowing a vast range of low voltages to be set in the BIOS. So despite its many appealing features it will soon be heading to an eBay near you 🙂

So the motherboard in question is the Soltek SL-865PE-L (the L on the end means it has onboard LAN). If you want to check out the detailed specification of this motherboard check out here. Yes it does have the most hideous colours on a motherboard you’ve ever seen but then I’m not one to show off my motherboard through a case side panel. More to the point, the can be picked up for £35 from eBuyer UK hence the reason I’ve got my mittens on two of them!

Just to summarise briefly, the board is based on the Intel 865PE north bridge and ICH5 south bridge (no RAID unfortunately). The heat sink on the north bridge is reasonably sized and importantly doesn’t use a fan. It does get quite hot but I haven’t yet encountered a problem with this. There a several aspects of this motherboard which make it ideal for use with Mobile Pentium 4 M processors. The first is that the VCore can be reduced right down to 1.1v. While on paper this isn’t as good as Gigabyte boards I am quite confident that the board is actually supplying what it says it is!

Secondly, you can set the default bus speed using jumpers. Normally motherboards automatically detect the correct FSB and you have to over/underclock in the BIOS. Of course with the jumpers left in their default position this is also the case with the Soltek but you can change this to force a 100, 133 or 200 MHz bus speed. This effectively does the same as the cutting the BSEL0/1 pin without making an irreversible change to your processor. Top Dorris!

It’s fair to say this isn’t a hardcore overclockers board. The fastest I got out of it was a FSB of 235.5 (2.82 GHz). Not bad but I know there’s would still be room in the processor and this is with a massive Zalman 92mm fan pumping air around the north bridge to see if that was the weakest link. I also attempted to do the trick of setting the FSB with jumpers to 133 MHz but increasing it to 200MHz (or whatever) in the BIOS. This enables PAT (the main difference between the 875 and 865PE chipsets) and vastly improves memory performance. The sweet spot I’ve found is running around 190MHz host clock which allows me to use a 1:1 FSB:RAM ratio and yet have my Geil value RAM, which was very cheap and is rated 2.5-4-4-8, running at 2-3-3-6. Not bad and certainly is better than overclocking the FSB to improve memory performance but at the cost of relaxed CAS timings.

So I guess what you’re all wanting to know is the temps Im getting now that the VCore is actually being altered, huh? Well…

1844.2 mhz

1844.2 mhz

Click here for the complete screenshot which will show that these temps are after running once through Prime95 to max out the core temp. Yes that really is an 1844.2 MHz Mobile Pentium 4M at a peak temperature of 33C! To put the data in to context, this is with my new Zalman 7000A-Cu with the fan at its slowest setting using the fan mate. At 1383 rpm it is very quite, although not silent. I figured that this would be a common setup and so a good indication of what you can expect.

This is the fastest I could get the processor to run without raising the VCore in the BIOS. You may notice that the reported VCore is actually 1.072v and it did jump around a bit. I’m still using that cheap PSU on the bench until a replacement arrives so I’m sure you could get better results with something that cost more than £5!

Note: I’ve since tested with my Q-Technology PSU which is far superior and I could push it faster at1.1v with this supply however I have not had chance to do any formal testing.

I should really round this with more recent testing and results but I’m not actually sure how much of this information is of any value to anyone anyway. Leave some comments if there are people out there who want more info.

I’m now using a Foxconn 865A01-PE-6EKRS which doesn’t actually allow for any VCore alterations in the BIOS. So I did another little pin mod trick on a 1.7GHz MP4M to hard undervolt it to approximately 1.15v. See this topic for more info.

It involves breaking or bending the AE1 pin so that it doesn’t make contact. With the VCore fixed I just pushed the FSB as far as I could before I encountered stability issues. I was surprised to see it went as far as 2.0GHz which is where it rests now, with an Arctic Cooling AC-FRZ-4 Freezer 4 running completely fanless! It’s an amazing heat sink for the price that’s for sure and the whole set up is doing me just fine for now.

28 thoughts on “Intel Mobile Pentium 4 M Exploration”

  1. Erik Wiemann

    Hi Will,

    Thanks for the great info. I have an Intel Pentium 4-M 2.4ghz I want to use in a 478 motherboard, and the information you have here makes it possible. Thank you!


    Erik Wiemann

  2. Wlll, found your webpages on using Pentium 4 mobile processors very helpful. I have a SL77P from a Dell laptop, I removed the BSEL1 pin to force a 200 fsb. It seemed to work fine in my Epox 4PEA motherboard. After I’d installed XP-pro however I experienced constant lock-ups and had to hard reboot. I’ve been changing the FSB and core voltage, which seems to have an effect. What would your reccomended voltage setting be for Vcore at 200fsb? I don’t want to overclock past the memory default speed (PC3200 Kingston value ram) just have a stable system running at around 2 – 2.4 ghz. If anything I’d rather underclock slightly for a stable system. I don’t appear to have any cooling problems and even with excesssive Vcore voltages the CPU temp never went over 44c.

    1. willdashwood

      I get some many hits on this guide and comment always appreciated. Makes me want to keep it updated!

      I would say you need a stable 1.3v VCore when operating at 2.4GHz (12×200) although this depends entirely on your set up and it can vary. For reference I’m running at 2.0GHz on 1.1v last time I checked. Have you also checked your RAM CAS timing settings? Make sure they’re OK for whatever frequency you’re running RAM at. At the end of the day it’s a case of trial and error I’m afraid. Try eliminating certain components out of the equation, such as RAM, by running it at very relaxed timings and lower frequency until you confident that’s not the issue. Same with graphics card or any other components you might have in there.

      I could do with squeezing some more performance out of my current rig so I will be attempting to get as fast as I can on around 1.3v. I’m hopeful that with my current set up I might reach 2.6 or 2.8GHz. Just enough to put off upgrading for a while.

  3. First, thanks for a great site. 🙂 The info on the P4-M has helped me a lot as I’m presently building a HTPC based on a 1.9GHz P4-M SL6DR processor. I had the opportunity to get one cheap and after stumbling upon these pages I decided to go for it.

    Unfortunately I made a mistake in my choice of motherboard (Asrock P4i65G). Running the CPU at 1.75V and not allowing undervolting makes me consider breaking the AE1 pin you mention. However, I’d like some more info and your link to the subject on Anandtec is unfortuately dead. I’d like to get 1.3V if possible, your 1.15V and 2.0GHz might be a little too low for my needs.

    On the upside, the Asrock P4i65G mobo actually supports SpeedStep and runs my P4-M at the correct 1.9GHz by default. I assume that means it runs at a mere 100 FSB with a 19 multiplier, which probably isn’t so great compared to a quad 200 = 800 FSB. I wonder what breaking the BSEL1 pin would do with my mobo that supports SpeedStep.

    With hope you still administrate this site, feel free to get back to me by email too.
    Best regards!

    1. willdashwood

      Well that does surprise me, you’ve come across the first standard consumer desktop motherboard to support SpeedStep as far as I’m aware. On the plus side if you did increase the FSB and kept the voltage as it is I reckon you could get well above 3.2GHz. Of course it would kick out a fair amount of heat so personally I’d look in to the AE1 pin mod to reduce the Vcore. I grabbed a copy of the forum post before it went down. I should really extract it’s info and put in on here but for now you can download the zip here.

    2. willdashwood

      Out of interest, does the Asrock P4i65G actually support changing the multiplier/VCore under different levels of load (the purpose of SpeedStep) or is it just fixed at the maximum?

      1. Thanks for the Anandtech pages! Hope I find sth useful there. 🙂

        I actually lost patience and bent the AE1 pin to see where it would take me. The result was 1.3V vcore and 10 degrees lower temp, according to BIOS. 🙂 Very satisfying, but I’m not sure if I can trust the BIOS readings. This mobo seem to have some quirks about it, that it identified the processor correctly and yet ran it at the incorrect voltage of 1.75V by default is only one of them.

        I’m still curious about what would happen if I removed the BSEL1 pin… I don’t think I’ll dare to do it without some more info, though. From what I’ve read, the SL6DR is not a great stepping for overclocking. Mine POSTs at 19×133=2533MHz, but I don’t know if it’s stable.

        The HTPC is still in its infant stage, the case and harddrive will arrive later this week. So far I have only done some testing with the mobo and processor, so I can’t really tell about the SpeedStep features. The manual doesn’t mention SpeedStep at all, there seem to be some discrepancies between the BIOS functions described in the manual and those I actually have in the BIOS. In the manual, there is the HyperThreading setting where I have the SpeedStep setting. Also, according to the manual, I’m supposed to be able to set the memory speed, but in my BIOS it is fixed.

        1. willdashwood

          I wouldn’t think you’ll get much faster than 2.6GHz on 1.3v but let us know how you get on.

          1. Now the HTPC is built, and I’m very happy. It’s virtually silent (more quiet than the ventilation in my apartment) and temperatures are acceptable although case temp is not great at 42-46 degrees celcius. CPU temp is constantly 5 degrees above case temp on idle and ~8 degrees above on load – as far as I can tell, I can only monitor CPU temp in BIOS. 🙁 XP-120 with 8,7dB Scythe 120mm fan seems to be doing a good job.

            I can unfortunately not get SpeedStep on the Asrock P4i65G to work. I set it from “disable” to “auto” in BIOS (no “enable” setting availible) only to find it back at “disable” next time I open BIOS.

            The P4i65G is not the best board for overclocking either. I can only change FSB for the CPU and only latency timings for the RAM. FSB/mem is locked at 3/5 divider(?), that is FSB is default at 4×100 and memory is 2×166. I run the CPU at 2280 MHz (FSB 4×120, mem 2×200) which gives no noticable increase in heat and is well above my needs. Roof is 2375 MHz (4×125, 2×208) with my cheap DDR400 RAM.

            I’m keeping an eye out for some faster RAM – it would be fun to see what this baby could do. 🙂

            Again, thanks for all the great info.
            I built a silent HTPC with great value with your help! 🙂

          2. Just a small update, might be off-topic so if you don’t want it to remain posted here I’ll understand. 🙂

            I managed to lower the case temp down to a very stable 39 degrees celcius by doing two things:
            – Turning the CPU fan, now blowing upwards (away from the CPU)
            – Removing the graphics card (Fanless Radeon 9250), now running the mainboards integrated graphics

            This put the CPU temp down to 44 degrees idle and 45 (!) degrees load. 🙂
            However, the biggest advantage is that my harddrives run about 7 degrees cooler now. This seems to have done miracles for the computers airflow/circulation. The HTPC even turned noticeable quiter! It seems that turning the fan (or accidently moving something in the process) cured some small resonance in the chassi.

            This is it. I’m happy! 🙂

  4. I have a gigabyte 8s651m-rzc and am looking at getting a p4 mobile 3.06ghz 1 mb L2 to put into this 533 mhz fsb motherboard. do you think I could get the full speed of this motherboard and processor. It looks like I can get the mobile processor cheaper than the non mobile processor. I have only overclocked my p4 2.4 512kb cache to 2.66. that is the only main experience I have playing with processor speeds and such.

    1. willdashwood

      I did have one of those processors but I can’t remember how well it performed. I sold it pretty quickly after getting it so let us know how you get on 🙂

      1. Hi, my old laptop PSU just died. The good old HP XE4500 was almost 6 years old! I got a 2.5GHZ Core Duo to replace it but I still see loads of potential in the old PC. I am planning to sell most components on e-bay but I would like to make a HTPC with the 1.7Ghz Pentium 4-M processor.
        I looked up the internet and I trust it is a socket 478 Northwood core. I trust a P4Dual-915GL or P4VM900-SATA2 motherboard will do the trick. The second one looks really interesting and is quite cheap. It includes an HDMI port as well as a 5.1 audio port and it is Vista ready.
        I think I could get a cheap system for under 100 GBP but I am a complete newbie so I’d need help to get things up and running 🙂

        1. willdashwood

          Both those motherboards should work fine though I have a preference for Intel chipsets from this era.

        2. AnimalsArentFood

          Some valuable information for anyone who owns a ASRock P4VM900 (P4VM900-SATA2) motherboard:

          Set “Thermal Throttling Temperature” to Disabled.
          Your system can be very badly choked if you don’t.

          – when the computer is starting up, press F2 to enter BIOS setup
          – go to the Advanced main menu
          – go to Chipset Configuration
          – set “Thermal Throttling Temperature” to Disabled

          I also highly recommend disabling “CPU Thermal Throttling”

          – go back to the Advanced main menu
          – go to CPU Configuration
          – set “CPU Thermal Throttling” to Disabled

          Remember to save changes before exiting BIOS setup.


          keywords: asrock p4vm900 sata2 mainboard lag low fps games gaming video poor slow weak bad wrong sucks stinks benchmark test performance clock speed pentium celeron p4 478 processor ghz problem bug error issue broken damaged conflict setting help faq fix

  5. Hi guys!
    Could you help me? I am in truble. I have bought three P4M processors till now (1,7 ghz – B0; 1,8 ghz – D1 ; 2,8 ghz – D1 stepping core and the last one is 533 fsb) and neather of them runs at 1,6 ghz, with a low voltage. If I make the vid4 pintrick, it runs at 1,08 volt, but at this volt can run only at 1,2 ghz.
    Suprisingly the B0 stepping core processor runs at 1,6 ghz, if I make the wire trick on the socket, at 1,17 volt, but it is not stable. Now I run it at 1,3 volt (using also the wire trick) and 1,6 ghz, but it runs at high temperatures (45 C when idle, and 51 when burns) and my fun has to run almost all the time, after the temperatures is higher then 45 C.
    I do not undestand why my processors doesnt run at low voltages, like yours do (at 1,05, or even 0,8) I would like to run it at 1,6 ghz in a 533 fsb motherbord (Mega PC 651) funless, but I can not. What is the problem with my processors???

    1. willdashwood

      Could it be that the PSU or motherboard isn’t actually feeding a correct stable voltage to the processor?

  6. hi’

    i’ve a couple of these p4-m cpus around.

    can you recommend some mainboards that would work – as the review was done a while back, maybe some of the boards are in the dumps.

    1. willdashwood

      I didn’t really keep up to date with s478 boards but I would say any based on an Intel chipset would be a safe bet. Full ATX boards tend to offer the most BIOS options and those aimed at overclockers better yet.

    1. willdashwood

      There shouldn’t be any problem just putting that processor in the motherboard without any mods.

      1. Hi There,

        Can anyone help I am a relative newbie with this kind of thing.
        I have a 3.2Ghz SL7DU Mobile P4 Prescott ( and am trying to run it in an ASUS P4R800-VM board, whilst the bios correctly recognizes the CPU the bios shows the board only feeding it 1.14V.
        CPUZ shows it as running @ 1.8Ghz with a multiplier of x14 instead of 3.2Ghz @ x24, I guess this is down to the voltage.
        Is it possible to do a volt mod on the CPU/Socket to bring up the voltage to 1.4V? and if so can anyone tell me what pins do I need to bridge/remove.

        Any and all help gratefully recieved



        1. willdashwood

          I’ve no idea why the motherboard has decided to run it at 1.8GHz. Due to SpeedStep it should be running at 1.6GHz (133 x 12). It will need more voltage (at least 1.5v, probably more) to run at 3.2GHz but if you read my article you’ll see that any P4M processor placed in a desktop motherboard that doesn’t support SpeedStep will use a fixed multiplier of x12 so in order to go faster than 2.4GHz you’ll have to raise the FSB accordingly. Of course I could be wrong but I’m fairly sure I had one of these processors and that was the case.

          1. Hi Will,

            Thanks for the info, looks like I’m done with this particular ASUS board tho as the Bios settings are very limited with no facility to alter the FSB.



  7. Web Designer

    Wow thanks !

    Times are tough and rather than buy a new machine I am pressing an older motherboard into service.. I didnt think this information would still around so thanks for keeping the positing up.


  8. this is cool stuff. i have an old non-functional laptop of the same processor but will need a spare desktop mobo to carry on with this experiment. i hope i find one. btw, Speedstep technology has been around since Pentium 3.

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