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Partition table and UEFI vs legacy?

pete6032

Diamond Member
Dec 3, 2010
5,042
869
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I am trying to install Windows 10 on an older laptop circa 2014. I made an install media using the USB creation tool and then booted to USB and I'm getting a message that "Windows cannot be installed to this disk. The selected disk has an MBR partition table. On EFI systems, Windows can only be installed to GPT disks."

Can someone explain what the problem is here? I don't care about any of the data on the disk so I'm happy to format, but what is Windows telling me?

Secondly there seems to be two boot options to get to usb. One option is "legacy" USB boot. The other options is UEFI USB boot. Which of these options should I be picking when I boot up?
 

VirtualLarry

No Lifer
Aug 25, 2001
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What this generally means is, you've booted the install media, in a different "style" (Legacy versus UEFI), than your existing disk is partitioned for.

Generally-speaking, if you CAN use UEFI, DO IT. So, you've proven that your system and install media is UEFI-bootable.

The problem is that the disk that you are trying to install to, is MBR-partitioned/formatted (aka requiring "Legacy" boot).

You can take the easy but sub-optimal route, and choose to boot your install USB as "Legacy" (look into any boot menu hotkeys), OR, you can boot the USB install stick in UEFI mode, and then, at the disk selection screen, hit SHIFT+F10, to bring up a Command Prompt window, type DISKPART, hit ENTER.

You should be at a DISKPART> prompt.

Type LIST DISK, to see a list of disks. You want to erase the disk that you are installing to, right?

Type SELECT DISK #, with the number of the disk that you want to install to and erase. (Check that the size of the disk is correct.)

Type LIST DISK again, and make sure that your desired disk is selected.

Then, AND THIS WILL EFFECTIVELY ERASE THE DISK, type CLEAN.

Then type EXIT, and EXIT. That will exit DISKPART and close the Command Prompt.

You should still be at the disk selection / installation screen of the Windows 10 installer. Click "Refresh Disks" (Or "Rescan Disks", whatever the wording is). Then select the disk to install to, it shouldn't have any partitions visible. (If it does - you erased the wrong disk with DISKPART!)

Then select the disk and click Next.

Edit: BTW, it is highly recommended, if re-installing Windows, to physically DISCONNECT any other disks, OTHER THAN the one that you are installing Windows onto.

Edit: Jack's solution, to be sure, would work, and it would be easier, from the user's perspective. But UEFI booting, can have more security and features than Legacy booting, and if you ever migrate your OS installation eventually to an NVMe SSD, you are going to want an OS image that boots UEFI style.
 
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mv2devnull

Golden Member
Apr 13, 2010
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What Larry said.

Partition table is ... a simple table ... on the disk that lists where on the disk the partitions are.
MBR and GPT are two different formats of partition table.

If you boot Windows in legacy mode, then it can load itself only from a disk that has table in MBR format.
If you boot Windows in UEFI mode, then it can load itself only from a disk that has table in GPT format.
Additional data disks can have either format.
The installer's USB stick can boot in both modes.
The installer sadly does not have "wipe current table and initialize new" in its GUI. Hence you have to "manually" erase the old table as Larry described.
 

Steltek

Platinum Member
Mar 29, 2001
2,674
480
126
Since you are currently doing an initial new install, do yourself a favor and go with UEFI and use GPT partitions on all drives.

The older MBR partitions only support drive sizes up to 2TB, so if you plan to add a large boot drive (say, when it becomes affordable as prices continue to drop) or even a large secondary >2TB hard drive for data storage in the future you'll be saving yourself A LOT of work in the long run.
 

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