PowerShell: Check if System Uses UEFI or Legacy BIOS
Need to know whether a machine boots via UEFI or the older Legacy BIOS mode - for compatibility checks, dual-boot setups, or troubleshooting a boot issue? This one-liner reads it straight from an environment variable.
Prerequisites:
- Privileges: None
- Module: Built-in, no import needed
Quick Command:
$env:firmware_typeExample Output:
UEFI📦
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How It Works:
- $env:firmware_type reads a built-in Windows environment variable that Windows itself sets based on how the system booted - it's not a CIM/WMI query, just a direct read of system state.
- The value returned is either UEFI or Legacy (sometimes seen as BIOS), telling you exactly which firmware mode the machine is currently running in.
- This is simpler and faster than digging through Win32_BIOS, since that CIM class doesn't actually expose this information directly.