Every PC contains a small chip that holds the BIOS (Basic Input/Output System) or its modern replacement, UEFI (Unified Extensible Firmware Interface). This firmware runs before Windows — it's what initialises your CPU, RAM, storage, and other hardware before handing control to the operating system.
Why UEFI Replaced BIOS
Legacy BIOS was a product of the 1980s with hard limitations: it couldn't boot from drives larger than 2.2TB, had no mouse support, and ran in 16-bit mode. UEFI is a full 64-bit environment with a graphical interface, support for drives up to 9.4 zettabytes, Secure Boot, and faster initialisation through parallel hardware setup.
Practical Things You Do in UEFI
- Enable XMP/EXPO: DDR5 RAM ships with a conservative profile; enabling XMP (Intel) or EXPO (AMD) unlocks the rated speed on the label
- Boot order: Set whether to boot from USB or SSD first — essential for Windows reinstallation or diagnostics
- Fan curves: Set temperature-based fan speed profiles for quiet or performance-priority operation
- Secure Boot: Required for Windows 11; prevents unsigned bootloaders from running
- Virtualisation: Enable Intel VT-x or AMD-V for Docker, virtual machines, and WSL2
Updating UEFI Firmware
Manufacturers release UEFI updates to fix bugs, add compatibility with new CPUs, and patch security vulnerabilities. Check your motherboard manufacturer's website periodically. Many modern UEFIs include a "EZ Flash" utility that updates directly from a USB drive without needing a working OS — useful if Windows won't boot.
What Not to Change Without Research
CPU overclocking settings, memory timing adjustments, and power delivery profiles can destabilise a system if set incorrectly. Don't change values you don't understand. Entering wrong voltage or frequency values for your CPU can cause immediate shutdown or, in extreme cases, hardware damage.