UEFI vs legacy BIOS boot explained

What you will achieve

Determine whether your PC uses UEFI or legacy BIOS boot, verify disk partition style matches that mode, and pick the correct USB boot entry before installing or repairing Windows.

1) Check how Windows is currently booted

1. Press Win + R, type msinfo32, and press Enter.
2. On System Summary, read BIOS Mode: UEFI is modern firmware boot; Legacy is old BIOS-style boot.
3. Note Secure Boot State — On indicates UEFI with Secure Boot (required for Windows 11 on most hardware).

2) Inspect firmware boot settings

1. Reboot and enter firmware setup — common keys: Del, F2, F10, or Esc (varies by vendor).
2. Find Boot Mode, UEFI/Legacy, or CSM (Compatibility Support Module). CSM enabled usually means legacy boot is allowed alongside UEFI.
3. UEFI installs require a GPT disk with an EFI System Partition (ESP, typically 100–260 MB, FAT32). Legacy installs use MBR with an active primary partition.

3) Verify partition style in PowerShell

Open Admin PowerShell (Win + X → Terminal (Admin)) and run:

Get-Disk | Select-Object Number, PartitionStyle, Size
Get-Partition | Where-Object {$_.Type -eq 'System'} | Format-Table DiskNumber, Size, GptType

PartitionStyle GPT with a System partition confirms UEFI layout. MBR with no ESP indicates legacy.

4) Match installation media to firmware

1. Create USB media with Microsoft's Media Creation Tool — it builds UEFI-capable installers automatically.
2. In the one-time boot menu, select UEFI: [USB brand] for UEFI installs. Avoid a plain USB entry without the UEFI prefix.
3. Windows 11 requires UEFI, Secure Boot, and TPM 2.0 on supported PCs. Legacy BIOS alone cannot install Windows 11 on most machines.

5) Troubleshoot boot mode mismatches

1. If setup says "Windows cannot be installed to this disk" on MBR, convert to GPT only when empty: diskpart → select disk N → clean → convert gpt.
2. Legacy OS on GPT or UEFI OS on MBR causes boot failures — match firmware mode to partition style before install.
3. After enabling Secure Boot, some Linux dual-boot entries disappear until you re-enrol keys or use signed shims — plan OS changes accordingly.

6) Verify boot files from Windows

bcdedit /enum firmware
bcdedit /enum {bootmgr}

The firmware entry list shows UEFI boot order entries Windows manages alongside vendor firmware.

Related guides

• Partition disks during Windows setup
• Install Windows with a local account