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: Microcodes are current as of 2018-12-02 (source). They were last updated by Intel on 2015-08-02.

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, 11, B1, or 91
    • 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:

  • cpu1067A_plat44_ver00000A0E_2015-07-29_PRD_A3107D75.bin
  • cpu1067A_platB1_ver00000A0E_2015-07-29_PRD_59BF808E.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.

mmtool cpu patch window

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.

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.

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.

Not sure how to update your 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

231 Responses

  • giusgius January 12, 201711:49 am

    My HP’s BIOS is .exe file and in that file there is BEN5.37 (1024kb BIOS file) and other .exe, .bat, .sys files…
    I extracted it and changed the BEN5.37 to BEN5.ROM to open with MTTool for adding microcodes but now I’m not able to use that BIOS.exe file to install, because I cannot repack it as it was official BIOS.EXE file…
    what can I do? How do you manage to do this mod if your BIOS is .exe file? Thanks in advance. #HELP

  • citizen January 13, 20176:13 am

    Thank you very much for writing this guide. I installed a Xeon E5450 on an MSI P35 Neo-2 FR using the sticker mod and modifying the socket so the cpu would fit. However, Windows 10 would still show my old E8600 (with only two cores) in the device manager and after manually removing it freeze on start-up. So I went back to my old E8600, downloaded the latest BIOS (Ver. 1C from MSI website) and added the respective microcodes as instructed in your guide, then flashed the bios using a FreeDOS bootable USB-Stick, finally did a CMOS reset via battery cut and reconfigured bios on first boot …. and what can I say, it worked like a charm. After first Windows boot there was still my old E8600 showing up (with only two cores) in the device manager as before, so again I removed it manually, then rebooted… this time Windows recognized the Xeon correctly with all 4 cores (so does CPU-Z) and has been running stable since. Performance increased remarkebly (e.g. no more lagging in Witcher 3). Thank you very much!

  • giusgius January 14, 20175:38 am

    I confirm E5440 working on my HP’s IPIBL-LB motherboard… That’s so cool…
    Thanks for your help. I really appreciate.

  • mahakali January 15, 20176:20 am

    Asus p5gc-mx gbl x5450 not running I can not find appropriate bios Help me

    • giusgius January 17, 20173:20 pm

      are you sure your motherboard supports these xen cpus or their corresponding Core 2 Quad ones? it only supports Core 2 Duo so you need dual core Xeon i think…

  • TNGOG January 17, 20171:30 am

    Has anyone manage to make a bio for a dell 745 that has 1066 speed, i would like to have a bio mod i can use to enable 45nm to use my e8400. can anyone help,?

  • Furba March 10, 20178:46 am

    Hi there …… remarkable site …… just want to add something that worked for me its an Dell Vostro motherboard, BIOS update is an .exe file, so if any one has a trouble to extract the ROM file, just start the BIOS updater(dont update, just start the updater) look at “C:\Users\YOURUSER\AppData\Local\Temp” there should be folder something like “_3450.tmp” or similar or just check for the newest folder …. rest is easy, get the file, mod it, replace the old one ……. now you can continue the updating of the BIOS ….. all new instructions, no noisy fan issue …. only fun ….. thanks to this guide!!!!!!!

  • kit0001 April 4, 20172:07 pm

    Help please find microcode updates for mobile Intel processors from the Intel site or another site.
    Thanks in advance.

  • Internet Power April 17, 201712:08 pm


    I am upgrading my machine’s CPU from C2D (LGA775) to Xeon (LGA771 Quad Core). Motherboard (Mercury PNMCP73V Version 1.0) supports 1333 FSB and support C2Q CPU’s and i am using RAM sticks 2*2GB (800 MHz). I already modified the CPU socket by be fully removing tabs which only supports LGA775 CPU. Now the Xeon LGA771 is able to install without any issue. But the main issue is that my machine freezes at the mercury logo. I already Mod the bios (AMI) with the new CPU Micro-codes but still my machine freezes. The previous C2D CPU is working fine but Xeon is not. anything i can try ? Thanks in advance.

    Motherboard’s BIOS is showing CPU’s multiplier 9 (FSB*multiplier = Speed of the processor)

  • Tomas May 3, 201710:29 am


    tried to add the E5450 (SLBBM) into my Dell XPS one A2010. The cpu is recognized without any mod but windows 10 wont boot. When i add the 771 microcode into the bios it wont start at all, just restarting by BIOS (no error message). To be hones Iam not sure if iam doing everything right. I have add this to the end of the cpu patch (its an AMI8 bios: cpu0001067a_plat00000044_ver00000a0b_date20100928 . If i do this the computer wont start… any suggestions? Tomas

    • Difo May 31, 20179:00 am

      You should add the both microcodes, for your 775 and additional for cpu’s 771 .

      I’ve added microcode for s775 firstly (plat00000011), and for s771 (plat00000044). And my Xeon X5450 works well. All instructions are present.

      • Tomas May 31, 20179:56 am


        thank you for answer. I already solved this but forget to post the answer here. I dont think its necessary to update also the LGA775 microcode, it doesnt make much sense mainly because the CPU is identifying according to the socket. Anyway, the problem was in the stepping. The A2010 cant handle the E0 stepping but can the C0 :) so,,, everything is working :) Toma

  • Difo May 31, 20178:53 am

    Thank you so much! I’ve done it successful with my MB P5P41T (non-LE/LX/Plus/etc, just clear P5P41T). It works well!


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