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Commonly confused · IT Support & Hardware

BIOS vs UEFI: What's the Difference?

BIOS is the legacy 16-bit firmware that initializes hardware and boots from the MBR. UEFI is its modern replacement, offering a graphical interface, mouse support, GPT disk support for drives over 2 TB, faster boot, and Secure Boot.

BIOSUEFI
AgeLegacy (1980s)Modern standard
Boot disk partitioningMBRGPT (MBR via CSM legacy mode)
Max boot drive size2 TB9.4 ZB theoretical
Secure BootNoYes, verifies signed boot loaders
InterfaceText, keyboard onlyGraphical, mouse support
Execution mode16-bit real mode32- or 64-bit
RequirementNot supported for Windows 11Windows 11 requires UEFI with Secure Boot capability and TPM 2.0
Remember it

UEFI is the BIOS that grew up: bigger disks, Secure Boot, and a mouse.

Exam tip

Expect questions linking UEFI to GPT and Secure Boot, and Windows 11 upgrade failures caused by legacy BIOS mode or TPM disabled. CMOS stores settings, and the CMOS battery keeps the clock.

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