UEFI and a Dell OptiPlex 990


I do a great deal of work with virtual machines and perform all of my operating system development on virtual platforms. My desktop PC came with a 500GB hard drive. Using a virtualization program and creating a couple of production sized virtual machines will take up a great deal of that space very quickly.

A larger hard drive is one of the easiest upgrades one can make to a computer. I ordered a 3TB drive for my Dell OptiPlex 990 and had hoped to just plug and chug, but it didn’t work out that way. What I had found out that the default traditional method of BIOS hardware management on the PC only allowed it to see partitions or drives no larger than 2TB. BIOS-based computers use hard drives that are partitioned in the Master Boot Record or “MBR” format. To use the new crop of large drives with more than 2TB of space, one needs to format the drive as a GUID Partition Table or GPT device. There, the largest of drives can be partitioned and formatted as one single volume, which is what I was after.

I should have just done my homework and just ordered a 2TB drive. Under BIOS/MBR, Windows setup would only see 2TB, leaving around 768GB unavailable. GPT disks cannot use the BIOS system. They rely on a newer system called the Universal Extensible Firmware Interface, or “UEFI.” The OptiPlex 990 has the ability to use a BIOS-based system or UEFI, but not both. Each are mutually exclusive to the OptiPlex 990. Newer computers have the ability to use UEFI with support for legacy BIOS system (UEFI-CSM), but not the 990.

I initially tried to get the 3TB HDD to be recognized by booting to a Windows PE boot drive and use DISKPART to partition and format the HDD as a GPT disk. Still, Windows setup would not use the drive. Windows 10 setup would indicate that setup could not use any available partition as they were in GPT format. The problem wasn’t the drive, which was set up correctly, it was the install media. I use an 8GB USB key drive to install Windows from an ISO file. A great piece of freeware called “Rufus” is what I use to make the boot-able USB key from the Windows ISO file. Rufus defaults to creating a Windows PE volume, which is what Windows setup is, that supports both MBR and UEFI with backwards compatibility. I though that would work, and it should have, but the OptiPlex 990 was BIOS or UEFI, not both. One option to create the USB boot key was pure UEFI.

While I was sorting this out, I noticed that when I switched the 990’s BIOS to UEFI mode, there were no more boot-able drives like the HDD, CD/DVD, or USB listed. This was accurate because none had been made available. The 3TB drive was GPT but did not contain any boot-able volumes at that point. I had yet to make a pure-UEFI USB key, and there was no disc in the DVD-RW drive, so no there were no UEFI boot options. Any and all BIOS/MBR, and UEFI/GPT boot devices are shown when the PC POSTs. As soon as I partitioned and formatted the 3TB drive as GPT, and inserted the all-UEFI USB boot drive, the OptiPlex 990 saw the USB drive as a UEFI boot device and Windows setup accepted the partitioned 3TB drive for install. After that, Windows 10 installed and I had ALL of the available space, which came in around 2.78TB.

To do…

Partition/format the drive as a GPT device.

Create a boot-able Windows PE USB drive and boot the target computer to it, with the larger-than-2TB-HDD installed.

Run DISKPART from the Windows PE prompt and enter the following commands to partition and format the drive as a GPT disk, minus the REM statements.

select disk 0
convert gpt
rem == 1. Windows RE tools partition ===============
create partition primary size=300
format quick fs=ntfs label="Windows RE tools"
assign letter="T"
set id="de94bba4-06d1-4d40-a16a-bfd50179d6ac"
gpt attributes=0x8000000000000001
rem == 2. System partition =========================
create partition efi size=100
rem    ** NOTE: For Advanced Format 4Kn drives,
rem               change this value to size = 260 ** 
format quick fs=fat32 label="System"
assign letter="S"
rem == 3. Microsoft Reserved (MSR) partition =======
create partition msr size=128
rem == 4. Windows partition ========================
rem ==    a. Create the Windows partition ==========
create partition primary 
rem ==    b. Create space for the recovery image ===
shrink minimum=15000
rem       ** NOTE: Update this size to match the size
rem                of the recovery image           **
rem ==    c. Prepare the Windows partition ========= 
format quick fs=ntfs label="Windows"
assign letter="W"
rem === 5. Recovery image partition ================
create partition primary
format quick fs=ntfs label="Recovery image"
assign letter="R"
set id="de94bba4-06d1-4d40-a16a-bfd50179d6ac"
gpt attributes=0x8000000000000001
list volume

Script from Microsoft

Create the all-UEFI Windows install USB drive…

Go into the computer’s BIOS by pressing F2 during the boot sequence (Dell), before Windows even starts to load. NOTE: BIOS/MBR disks will not boot in a UEFI/GPT configuration. Any change from BIOS/MBR to UEFI/GPT WILL REQUIRE a Windows reinstall. No way around it, so Back up your data.

On a separate computer, insert the USB key, and open Rufus as an admin.

The USB key should be listed in the top dialog box, make sure you’re formatting the right drive if there are multiple USB drives currently inserted into the PC. From the bottom part, near where it says “Create boot-able disk using [ ISO Image]”, click the small button with the disc and drive icon and choose your Windows install ISO.

Next, select the drop-down menu option under “Partition scheme and target system type”, choose “GPT partition scheme for UEFI.” If the source ISO file changes, the partition scheme changes also, so watch that.

RufusCreate the drive and insert it into the computer that has the large HDD and boot to it by pressing F12 (Dell/Lenovo). If the USB key was created properly as a UEFI device, it will show up as a UEFI boot option under the BIOS boot options which will still be the CD/DVD drive and the HDD (possibly).

Install Windows and relish in the large space now available!


25 thoughts on “UEFI and a Dell OptiPlex 990

  1. hi, i run some Optiplex’s 990 at the office and at work, so i was struggling with the same problem.
    I simplified this to this using old school tech… burning a Windows 10 setup DVD from the anniversary ISO download. (honestly I never burned a DVD since 1999)
    1) Setup the BIOS to UEFI
    2) Start the windows setup booting from de DVD
    3) Pres shift-F10 to get a command prompt
    4) DISKPART: select disk 0, clean, convert GPT
    5) Exit diskpart, exit command prompt
    6) Continue setup
    Now UEFI Works 😉

  2. Very helpful indeed. I have just installed an SSD into a Dell Optiplex 990, with the intention of adding a 4TB hard drive also (if the 15mm height on a 2.5 inch drive will fit).

    I also did the same – I burnt a DVD of Windows 10 Anniversary Edition, and installed from that. Choose UEFI mode in the latest BIOS (A19) and you’re well away. Use DiskPart to clean and format the SSD. Install Windows 10 on your new GPT partition.

    Job done!

    Thank you for writing this article – very helpful indeed.

  3. I’m not sure what type of case your 990 has, but we use mostly the small form factor (SFF). I haven’t really been able to get 2 drives in that case. One time, in a pinch, we taped the SSD to the outside of the case just to get data off. I’m glad you enjoyed the article! Thanks for visiting!

  4. Hi Jason,

    My OptiPlex 990 also has the small form factor (SFF) case. There’s enough space inside for one 3.5″ hard drive, or two 2.5″ drives. Having installed the 2.5″ SSD, I now realise that I’m limited to one additional 2.5″ drive – IF I use the ‘official’ Dell drive caddy, which I have.

    I’m now seriously considering putting the original 3.5″ drive back in the drive bay, and finding somewhere to Velcro the 2.5″ SSD inside the case, which – although tight – looks like it might be a distinct possibility. I’m thinking that the top of the PSU could be an option. Although I dislike ‘Heath Robinson’ (or ‘McGyver’ in the USA!) approaches such as this, it’s the only way that I could have an SSD and a 7200RPM 4GB hard drive inside the chassis.

    Watch this space!

    Best Regards,


  5. I once fixed an SSD in the place of the DVD-ROM, which I never seem to use anymore. That worked well, while I needed it. The only thing I would be cautious of, when adding stuff inside one of those SFF cases is airflow. Those things are designed to be laid out a certain way, so that they can run cool.

  6. so i dont want to appear simple but is there anyway someone can make a video because i have a 6tb just collecting dust that i bought a couple months ago and almost gave up hope installing but i dont think i quite am getting what you guys are writing. i learn better by watching.

  7. Sure. Can you provide screen capture software? Why not just use the 6TB as a secondary drive, and install Windows on a smaller drive?

  8. Wow, this really came in handy. I was in the same situation, trying to get my used Optiplex to recognise and install Windows to a 3TB drive I installed, and after seven tries of installing Windows, I finally got all the pieces in place. I did end up following a lot of your steps here, including using Rufus to create the UEFI install drive, but found at the end, when trying to boot from the USB drive, I needed to go into the UEFI boot config to set up the USB drive as a boot device, but once the install completed, everything worked without hassle.

  9. No screenshots, but all you have to do is set your PC’s BIOS to use UEFI only (no legacy or compatibility mode). Create your Windows installation media on a USB key that is formatted for UEFI only (check out Rufus.io). Boot the PC with all of that in place, including your 4TB HDD and start the Windows installation. The UEFI install key, running on the PC w/UEFI BIOS set should pick up the 4TB HDD. If not, run diskpart on the 4TBHDD to convert it to GPT and then manually create the partitions on which to install Windows.

  10. Used Rufus. Created GPT UEFI USB with win10 ISO Set Samsung 500GB SSD to GPT… UEFI boot seq only shows wndows boot manager-not SSD. Wont boot Windows.. Says no bootable drives.. (SSD shows in bios drives config) Any thoughts?

  11. After countless hours of reinstalling Win10, and attempting to change bootmngr in C: Prompt with no avail, I finally found the answer.. Follow steps below to initialize the SSD prior to clean install for bootmngr to recognize and successfully boot.

    Before you can use your new SSD you have to initialize and partition it. Follow the below process, unless you are performing a clean installation of your operating system, or cloning to your SSD, both of which normally do this for you. Note: if you simply need to format/reformat a drive, only steps 5-9 below will be needed, assuming your SSD has previously been initialized.

    1-Attach the SSD as a secondary drive and load Windows from your existing drive.
    2-In Windows 7 and earlier, open ‘Disk Management’ by right clicking on ‘Computer’ and selecting ‘Manage’, then ‘Disk Management’. In Windows 8 and later, move the mouse to the lower left corner of your desktop and right-click on the Start Icon, then select Disk Management.
    3-When Disk Management opens, a pop-up should appear and prompt you to initialize the SSD.
    4-Select MBR (Master Boot Record) or GUID partition table (GPT) and click OK. MBR is best for certain legacy software compatibility, while GPT is better for modern systems.
    5-Right click in the area that says Unallocated and select New Simple Volume…
    6-The New Simple Volume Wizard will open, click Next
    7-Leave the Specify Volume Size as the maximum (default value) and click Next
    8-Select a Drive Letter and click Next
    9-In the Format Partition screen, decide on a Volume label (the name you want to give the drive) and click Next

    The drive is now formatted and ready for use.

  12. Hello. I have the same problem. I follow your suggestions but when the windows installation start, it stucks in the windows logo.

    I wonder if it takes very long in this step. How long takes in your computer?

  13. Could it be a drive issue? If the PC wasn’t able to see the drive at all because of a MBR/UEFI settings conflict, you wouldn’t get to the logo at all. Did you try to convert the drive from an MBR to GPT/UEFI?

  14. Hi Jason (and others),

    Nice thread. Been going for a while so hope it’s still active.

    I too have a dell optiplex 990 with a 2.5 inch 128GB SSD primary (boot) drive with Win7 64bit. I want to re-purpose this machine and try it out as my IPCAM NVR. Thus I need more HDD space. I just took it apart and saw it has 3 sata interfaces on the MB. I found I had a very old 300G 2.5 in HDD from an older ACER laptop I got asked to recover data from (i’m that IT guy in my family) and plugged it into the 3rd cream coloured sata interface and it worked fine (the blue sata has my OS SSD drive, the black sata has the DVD).

    I am wanting to add a 3TB as my second drive when I came across this thread. Am I understanding correctly that I won’t have any issues with using a 3TB as my 2nd HDD (i.e. won’t be booting off of it)? Or will I still have to convert it to GPT as per this thread?

    Also, bonus question, anybody know what the different SATA interfaces on the Optiplex 990 MOBO mean?



  15. I just got a Optiplex 990 with an i7-2600 (no delid needed!) at $100 shipped. Other than a couple minor scuffs, looks like a new PC & has pased all of the pre-boot tests (no OS installed, yet Windows 7 Pro COA is affixed).

    These are true workhorse PC’s, wish I’d had known of these before purchasing an XPS 8700 (with fake x4 slot). The Optiplex 990 has a true x4 slot, although PCIe 2.0, will try to install Windows 7 using a 240GB MyDigitalSSD BPX (Phison E7 controller). If I can’t install to this, will follow these instructions with a 256GB Samsung 850 Pro & WD RE4 500GB as a data drive.

    Gigabyte has a tool to insert NVMe & USB 3.0 drivers (the latter not needed for this PC) into a Windows 7 through 10 ISO’s. Can even install to already created bootable media. Won’t be updating the BIOS due to issues others has reported with NVMe drives afterwards, leaving system unbootable & no way to turn back the clock.

    I think I’ll love the Optiplex 990!


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