Converting Win7 from MBR to GPT, Part 1

The HP Omni 220 Quad has UEFI but comes installed with Windows 7 in legacy BIOS mode. Why? Who knows.  But we can fix that.

This is the first part of a 2-part series describing how to convert a 64-bit Windows 7 install from MBR to GPT, allowing the OS to take full advantage of UEFI’s advanced features.  This post provides some background on BIOS, UEFI, MBR, and GPT.  It also describes how to backup your Windows install, in case anything goes wrong.



All the latest motherboards use UEFI instead of BIOS. This the low-level software that checks connected hardware, finds and loads bootloaders, and tells the OS what hardware is connected. When you start your computer, you’ll see lines of text before the operating system starts to load: this is the UEFI or BIOS.

UEFI supports some useful features that BIOS does not:

    • GUID Partition Table (GPT)
    • Hard Disks >2TiB
    • 64-bit CPU & OS
    • Faster boot-up

BIOS is limited to using an MBR partition table and only supports 16-bit processor mode at boot-up. The MBR supports only 1 bootloader per physical disk, which resides at the beginning of the disk. Even worse, it only supports 4 primary (bootable) partitions. If you want more than 4, you have to use extended partitions which can’t be accessed by some bootloaders.

So UEFI/GPT is better than BIOS/MBR.

To make the transition easier, most UEFI implementations can boot MBR disks in a BIOS-compatibility mode. That means you can install a legacy OS that only understands MBR and it will still work.

Unfortunately, HP decided to install Windows 7 in BIOS mode on some of its UEFI-based computers (including the HP Omni 220 Quad). Why? Who knows. Windows 7 64-bit is fully UEFI-compatible.

This wouldn’t be such a big deal except that their Windows install uses 3 partitions:

    • Boot Partition
    • Windows Partition
    • HP Recovery Partition

That’s 3 out of 4 primary partitions. While you could create some extended partitions using the last primary partition, it is not an ideal situation. There’s only one thing to do: convert the disk from MBR to GPT & make sure Windows still boots.





The first step is tedious but important. If anything goes wrong it’s nice to know that you can return to a known-good state. A good backup frees you from the fear of permanently breaking something. It’s a comforting feeling.

In addition to creating a backup, the C: partition needs to be shrunk to allow for a UEFI system partition.

    1. Defrag
    2. Shrink Partition
    3. Backup



Before creating the actual backup, it is helpful to consolidate the data on the hard drive. Defragging your computer is like cleaning your desk: all your files and folders are consolidated and organized, and you may actually have more space to work with afterward.

A word for those with SSDs: solid state disks don’t need to be defragmented. If you want to know why, read this article.

For defragging, I recommend MyDefrag. It’s got a lot of good features and can run automatically.


Shrink the Windows Partition

Your Windows partition probably takes up all the available space on the disk. We’ll need some of that for the UEFI System partition and any other partitions you may want to create.

Click on the Start Menu and type “partition” into the search box.

Select “Create and format hard disk partitions”. The Disk Management tool will open up.

Right-click on the C:\ drive.

Select “Shrink Volume…”

You will be asked for how much space to remove from the partition (in MB). Determine how much space you want left on your HD (I left 250GB or 256,000MB) and subtract that from the total size. That will leave you with the number of MB to shrink the partition by.


Create a System Image

Windows 7 comes with a tool that will back up all your windows partitions at once.

1. Go to: Control Panel –> Backup & Restore

Backup and Restore

2. Click “Create a System Image”.

3. Select “On one or more DVDs” and click Next.

4. Click “Start Backup”.

Now your backup is in progress. When prompted, insert DVDs.  My 74.5GB windows system took 8 dual-layer DVDs.

With backup in hand, you can now proceed to the conversion process.


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