How to Update CPU Microcode in an AMI BIOS – For LGA 771 & 775



In this guide, we'll show you how to update or add new CPU microcode to an AMI BIOS. If you have an Award or Phoenix BIOS, check out this guide instead.

Note: This information has only been tested with LGA 771 and LGA 775 BIOS files, so if you have a newer motherboard (especially UEFI ones), it probably won't work.

Why would you want to do this?

Updating the microcode is helpful if:

  • You did the LGA 771 to 775 MOD, and your Xeon is not working as expected (or is missing functionality, such as CompareExchange128, Speedstep, SSE 4.1, or VT-X).
  • Your BIOS doesn't support a newer processor that you want to run.
  • The microcode for your processor is old and may be buggy.


There's an element of risk just flashing a normal BIOS, and especially when you start modifying it, so please attempt this mod at your own risk (and only if you're experiencing some problem). We highly recommend that you don't flash the modified BIOS unless you've verified the microcode was added correctly. If you accidentally remove the microcode that your processor needs, your system may fail to boot. We are not responsible if your system is damaged while attempting this.

Things you'll need

Step 1 - Download the microcode for your platform

  • Desktop LGA 771 and LGA 775 microcode
    • If you're trying to add LGA 771 Xeon support to an LGA 775 motherboard, this is the recommended file to download. It will allow you to not only add the LGA 771 Xeon microcode to your BIOS, but you can also update your processor's similar LGA 775 microcode (which is probably a good idea).
    • Contains microcode for all Core 2 Duo and later desktop processors (no Pentium 4 or mobile support)
    • Contains microcode for all LGA 771 Xeon processors (except older Pentium 4 based 50xx models).
  • Desktop LGA 775 microcode
    • Contains microcode for all Core 2 Duo and later desktop processors (no Pentium 4 or mobile support)
  • Mobile LGA 775 microcode
    • Contains microcode for all Core 2 Duo and later mobile/laptop processors (no Pentium 4 or desktop support)
  • LGA 771 microcode
    • Contains microcode for all the LGA 771 Xeon processors mentioned earlier (no LGA 775 or mobile support)

Step 2 - Look up the CPUID for your processor

You'll need the CPUID to update the right microcode (how to get the CPUID).

What if I can't find the CPUID for my processor?

You can just update all of the microcodes.

Step 3 - Set aside the microcode files for your processor's CPUID

Note: If your CPUID ends in an "h" and you don't see a microcode with an "h" on the end, just ignore the "h" because it isn't actually part part of the CPUID. That just means it's a hexadecimal number.

When you unzip the microcode file, you'll see a bunch of individual microcode files that have filenames like this:


Here's what the different parts of the filename mean:

  • cpu0001067a - 1067A is the CPUID that is supported by this microcode
  • plat00000044 - plat is short for platform. This tells which sockets are supported by the microcode.
    • LGA 771 microcodes have a 4, 40, or 44 in this section
    • Desktop LGA 775 has a 1, 10, or 11
    • And for mobile LGA 775 it's a 20, 80, or A0
  • ver00000a0b - a0b is the version number
  • date20100928 - 2010-09-28 is the date the microcode was last updated

Which microcode files should I set aside?

You'll want to set aside all of the microcode files with your processor's CPUID. There should be at least one of these for each platform, and you should go ahead and update the microcode for all of the platforms that you want your motherboard to support.


So for our E5450 (E0 stepping SLBBM) with a CPUID of 1067A, here are the LGA 775 and LGA 771 microcode files with a CPUID of 1067A:

  • cpu0001067a_plat00000011_ver00000a0b_date20100928.bin
  • cpu0001067a_plat00000044_ver00000a0b_date20100928.bin

If you have that processor and want to add the LGA 771 microcode and update LGA 775 microcode (which is recommended), you'd want to set aside both of these files.

Step 4 - Open your BIOS in MMTOOL by using the "Load Rom" button

Note: MMTOOL will only open BIOS files that end in .ROM, so if yours doesn't, just rename it to .ROM for now.

Having trouble finding the BIOS rom file that you need to MOD?

If your BIOS is in an .EXE format

You'll need to first extract it with an unzipping program like 7-Zip. Then look for a file that ends in .BIN, .ROM, or possibly something else like a number. LGA 775 BIOSes are usually around 1024 KB in size, so look for a file about that size. You can also try to open the file in MMTOOL. If it isn't the right file, MMTOOL will let you know.

How to extract the actual BIOS from a Dell .EXE file

Execute the following command from a DOS command prompt window:

DellBiosFilename.exe /writeromfile

This should extract the actual BIOS file to the same directory. When you're done modding the BIOS, you can use a program called AFUDOS.EXE to flash a Dell AMI BIOS.

mmtool cpu patch window

Step 5 - Click the "CPU PATCH" tab to access the microcode area of the program

You'll then see a list of all of your current microcodes.

Step 6 - If you're updating your old microcode, delete all of the old microcodes that match your processor's CPUID

Note: MMTOOL only shows the last 4 characters of the CPUID, so don't let that throw you off.

  • Select the option "Delete a Patch Data"
  • Click the microcode you want to delete
  • Click the Apply button

If your Xeon's CPUID is 1067A, then delete all of the microcode entries with a CPUID of 067A (there may be more than one due to different platform types).

Step 7 - Insert the new microcodes

  • Select the option "Insert a Patch Data"
  • Click browse and select the microcode you want to insert
  • Click the Apply button

Do this for all of the microcode files that have your processor's CPUID. You should have set these aside in an earlier step.

What should I do if I'm getting an error message that there isn't enough room for the microcode?

You'll need to delete some of the old microcodes to make room. Just make sure you keep the microcode for your old processor in case you ever need to reinstall it.

The microcodes with a CPUID of 066x (where x can be any letter or number) are usually older Pentium 4 and Celerons, so those are usually safe to delete. You can also search for the CPUID on cpu-world to find out which processors use that CPUID.

Step 8 - Click "Save ROM as.." to save your modified BIOS

Step 9 - Verify that the microcode was added correctly

Go ahead and close MMTOOL, reopen it, and load your modified BIOS file, which you saved in the previous step.

Navigate to the CPU Patch tab again, and make sure all of the microcodes that you added earlier are shown and that the date on them is from 2010 (which is when Intel last updated them).

You should also check to make sure no old microcode for your CPUID is present. If it is, you'll need to go back and delete it. Otherwise, your system may use the old microcode instead of the new ones we just added.

Step 10 - Update your BIOS using the modified ROM file that you just created

You should be able to update it the same way you'd update a normal BIOS.

I'm not sure how to update my BIOS

The method for updating your BIOS is different for each motherboard manufacturer.

  • With some, you can simply put the BIOS file on a USB key, reboot and enter the BIOS, and update it from there.
  • Others may have a BIOS updating program that you can run from within Windows.
  • And in some cases, you may need to put the BIOS on a bootable DOS USB key, CD, or DVD and update it from a command prompt.

If there's a Windows or DOS BIOS updating program, it will usually be included with the BIOS or mentioned when you download the BIOS. If you don't see it, check the downloads section, FAQ section, or support section.

If all else fails, try searching Google for your motherboard’s model and update BIOS or something like that.

Step 11 - Do a FULL BIOS reset (use the 3-pin motherboard reset jumper, and then load the default BIOS settings on the first startup)

How to fully reset your BIOS

206 Responses

  • Peter May 6, 20157:28 pm

    Hey, i got an E5450 for my Asus p5b-e mobo.

    I modded latest 1807 bios release using both 44 and 11 platform bin files for 1067A and deleted the old one.

    I used asus upgrade utility to flash it and i got my bios corrupted… got error when it was verifying (last step).

    I rolled back to an earlier bios version and i am using my old cpu.. but i am a bit afraid now to move on, so i want your kind help.

    What am i doing wrong guys?

  • Sizz May 7, 201511:26 pm

    P5Q-E & X5460.

    I used Ket’s 5th Anniversary Final bios and added the LGA771 microcode. BIOS is not letting Windows boot. It hangs at the logo.

    If I flash back to original Ket’s BIOS, everything is fine and will boot normally.

    I’ve tried clearing bios plenty of times, flashing multiple variations of adding microcodes (updating LGA775 and LGA771 codes) to the BIOS, but still won’t work.

    I prefer to use Ket’s BIOS due to the fact that he has modded it for better and more stable performance.

    Any idea?
    Or rather, anyone could mod me a proper KET’s 5th Anniversary Bios?


  • Joan May 29, 201511:52 am

    Anyone knows how to access a DELL AMI BIOS?
    It’s from a Vostro 220s, motherboard G45M03:

    – renaming to .ROM doesn’t work for me (trying to open with MMtool 3.22)
    – trying to open/test the archive with 7-zip (v9.2) doesn’t work either
    – running ‘Vx20-130.EXE /writeromfile’ in a command window doesn’t produce any output, but UAC comes up asking if I want to allow that file to make modifications..

    I’m running Windows 7 Home Premium 64Bit testing this.

    • Jon August 23, 20154:51 pm

      Hi, I’m having this exact problem with my Vostro 220. Did you manage to solve it?

    • Tim Small September 17, 20158:06 am

      The .ROM file is left in the directory by the programmer. The programmer exe is deleted by it, but can easily be undeleted. Both are here if you want to try and mod them:

    • Sildur December 18, 201510:26 am

      Here are the unmodified but unpacked files from the vostro bios 1.3.0:

      I put the Vx20-130.exe on my DOS USB stick and run it on a none dell pc. What it does is it unpacks the files but doesn’t install them since it’s not a dell pc. After booting back to windows you should find those files on your USB stick now.

      To flash it boot back into your dos system and type in AFU877.exe RomName.rom and press enter, it will then flash the bios.

  • Daniel Molina June 2, 20154:45 am

    do have to insert all the codes or just the one that match with your cpuid

    • Sunday June 12, 20153:08 am

      Just the one you’re using. To stay on the safe side just insert all the codes matching your CPUID.

  • gregg June 13, 20157:08 pm

    Having trouble updating the modified BIOS on an ASRock P5B-DE using the ‘Instant Flash’ CMOS method (only option) for adding X5460 microcodes. It recognizes the file, but then hangs while “Checking” the file. Have BIOS 1.30 (latest) installed, but doesn’t have the X5460 mircocodes. Followed your advice above, even thinking the issue was related to size by deleting an unused file of the same size I added, but still keeps endlessly ‘Checking’. Could I use some Windows based BIOS flash utility to force it in? It is an AMI BIOS. Original file, from ASRock site has a ‘.#0’ extension instead of ‘.rom’. Tried both extensions, but no luck. Any ideas?

    • gregg June 14, 201512:27 am

      Forced it using the DOC AMI BIOS tool and everything is working now…and significantly faster too.

  • Loreta June 24, 201511:03 am

    Updatet microcode on Asus P5K, instaled new bios with Asus update and everything works perfekt. Have instaled e5450. Just folowed instructions, thx.

  • Adam September 17, 20152:38 am

    Interesting problem…..I updated the microcode on my MSI P35 Neo board’s bios, flashed the bios, but now I just get a blank screen on startup (in other words it doesn’t even boot to bios) unless I reset the cmos each time. It’ll then start, and I can hit f2 to get it to boot to the hard drive, which presumably sets the defaults in the bios, but, if I hit f1, and actually go to the bios and set everything up (date, time, boot order) and restart, it still won’t do anything, and I have to reset the cmos to get it to start. Any ideas?

    • Adam September 17, 20152:43 am

      Basically the motherboard won’t do anything unless I “fully reset the bios” each time I want to start it, and that’s not going to fly, because the whole point of doing this is to put my X5450 in and overclock it…..right now it’s still got a Q9300 C2Q in it.

      • Ekkehard November 6, 20159:57 am

        Same problem here. First i thought it might be because of multiple capacitors i had to change (they were close to bursting) . Now i changed the bios battery hence its ten years old.
        I would like to know what happens to the bios when i write to it, i.e. save my settings.
        No idea.

        • Ekkehard November 6, 201510:00 am

          You don’t need to update the microcode, by the way. Just flash the BIOS version 2.1 from the MSI website. It already contains microcode version A0B as reported by hwinfo64.

  • garmin October 3, 201512:22 am

    I wonder how to add microcode into the G41SN824.BSS bios file (Biostar G41D3C). CBROM and MMTOOLS don’t recognize it. Thanks.

    • bels November 4, 20151:56 pm

      rename it to “G41SN824.rom” load it with mmtools, edit and save it. rename it again to “G41SN824.bss”..
      for my personal experience,(with my biostar g31m7-te, forgot to rename it again to biosname.bss) .rom extension still recognized by afudos. success just second i’m writing this. will update info with x5260 next..

    • Oviedo January 21, 201711:33 pm

      Hello friend! I also have a mainboard BIOSTAR G413DC, I would like to know if
      did it work for you,
      and what procedure followed?

      Thank you

  • Oskar November 4, 20151:57 pm

    I have a xeon E5420 and a vostro 220. The cpu works and is detected by the bios, but the fans run at full speed and i cant get into windows 10. I can boot into Hirens Boot CD and launch cpu-z and i see that i dont have SSE 4.1. This is why i cant boot into windows 10. So i have put back my old E8400 to get the cpu microde for my bios but i am stuck at step 4 where i cant get the rom file. I have tried running this command: DellBiosFilename.exe /writeromfile (with the correct exe name ofcourse) but that does nothing, so i cant get the dell rom file. I see that others have been able to run the vostro 220 with the xeon E5450 which is very simular to my E5420, so i must be missing something.
    How do i get the dell rom file?

    • Oskar November 5, 20152:56 pm

      Was able to flash a modified bios. No more noisy fan and windows 10 boots. But now i have another problem, the computer is super slow. With the E8400 its lightning fast.

      • Koen Delvaux December 13, 20157:05 am

        I did the same on a Vostro 220s, switched from E8400 to E5450 with modded bios. Super slow in Windows 10 due to DPC latency >15000, 30% CPU usage when idle and mouse pointer refreshes only about once per second. However: when booting into Safe mode, the system works like normal. I have OS X on a second HD and that also works normal, no problem, fans and cpu stepping work like normal and very fast performance.
        So, there must be something that Windows 10 loads in ring 0 that is not catching IRQs or not dealing with them properly due to some cpu instruction mismatch.

        • Sildur December 18, 201510:42 am

          Any news on this, or are we just unable to make use of windows? The stuttering even happens in win7 32bit. Also noticed core 3 and 4 are not used at all while core 1 and 2 are going up and down constantly.

          Will try Linux mint next…

          • Stojke February 27, 20164:59 pm

            Any update on this?
            I have moded an E5430 into this machine (Dell Vostro 220) and inserted and removed microcodes a lot of times (different combinations) for a few hours. The system is still sluggish and slow.

            Is there something to remedy this, I know some one managed to run an e5420 perfectly fine.

          • Sildur February 28, 20161:19 pm

            Ended up going with another Mainboard. That Dell just doesn’t work well. This site should remove it from the compatibility list.

    • Alin March 5, 201710:06 am

      So, you fixed it ever since?
      I also run E8400 and want to uprade to a Xeon E5420, on a ASUS P5Q Deluxe.
      If you managed to make it work, reply if you can and let me know if there was any real improvement over the Core Duo E8400.Cheers!

  • bels November 4, 20152:24 pm

    yep.. g31m7te now boot with x5260. updated all microcode (771 and 775).. wasn’t boot with e8600 either.. in case someone need to know..


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