Overview
Whether a PC boots through modern UEFI firmware or legacy BIOS compatibility mode quietly determines eligibility for several important Windows features — Secure Boot, fast boot, GPT disk support beyond 2TB, and Windows 11 compatibility all depend on running in genuine UEFI mode rather than legacy BIOS emulation. UEFI Legacy Boot Checker reports which mode your specific system is currently using, without requiring a reboot into firmware setup to find out.
Key Features
- Reports whether the system booted via UEFI or legacy BIOS
- Checks the same underlying signal Windows itself uses for compatibility checks
- No reboot or firmware setup screen access required
Why You Might Need This Tool
Firmware boot mode is a frequent, hidden blocker for Windows 11 upgrades and for Secure Boot in general, since Secure Boot and modern security features are simply unavailable while a system runs in legacy BIOS mode, regardless of what the actual hardware is capable of. It also matters when converting a disk between MBR and GPT partition styles, since the two are tied closely to boot mode, and mismatching them is a common cause of a system that suddenly refuses to boot after a well-intentioned disk conversion. Confirming current boot mode before attempting any of these changes avoids a nasty surprise.
How It Works
The tool checks for the presence of the
HKLM\SYSTEM\CurrentControlSet\Control\SecureBoot\State registry
key — the same key Secure Boot Checker reads — since this key is only ever created
by Windows on systems that booted through UEFI firmware; its complete absence is a
reliable indicator the system is running legacy BIOS instead. As a secondary
cross-check, the tool also reads the firmware_type environment variable
where available, which some Windows versions populate directly with "UEFI" or
"Legacy" as an explicit confirmation.
How to Use It
Open the program and firmware boot mode is reported immediately with no configuration needed — no reboot into firmware setup is required for this check.
System Requirements & Notes
Runs on 64-bit Windows 10/11 with no administrator rights required.
Frequently Asked Questions
Can I switch from legacy BIOS to UEFI without reinstalling Windows?
In many cases yes, using Windows' built-in MBR2GPT conversion tool
followed by switching the firmware setting, but this is an advanced operation that
carries real risk of an unbootable system if done incorrectly — back up first.
Why does my brand-new PC show legacy BIOS mode?
Some systems ship with a Compatibility Support Module (CSM) enabled by default for
broader compatibility with older operating systems; disabling CSM in UEFI firmware
settings, after confirming your installed OS supports it, switches to full UEFI
mode.
Does UEFI mode alone guarantee Secure Boot is enabled?
No — UEFI mode is a prerequisite for Secure Boot, but Secure Boot itself is a
separate setting that must still be explicitly enabled; check
Secure Boot Checker to confirm both.