UEFI BIOS explained

Darien Graham-Smith explains how the flexible UEFI BIOS system brings computing up to date

If you’re buying a new PC, you'll see systems described as boasting a UEFI BIOS. If you’re building a computer from scratch you may notice that some motherboards feature a UEFI BIOS, while older models lack it. But what does UEFI mean, and is it worth paying extra for it?

Why BIOS needs replacing

Anyone who has used a PC will be at least vaguely familiar with the BIOS – the Basic Input/Output System that’s stored in your PC’s firmware, and which kicks in as soon as you turn on your PC. Before the operating system loads, it’s the BIOS that handles the fundamental business of enumerating which hardware is installed, and applying basic settings such as CPU frequencies and RAM timings. By accessing the BIOS’ built-in menu, you can adjust various controls to (for example) make components run at different speeds, or configure your PC to boot from a different disk.

Broadly speaking, the role of the PC BIOS hasn’t changed in more than 20 years, and for most of that time it’s done a satisfactory job. But as PC technology has advanced, more features requiring BIOS support have appeared, such as remote security management, temperature and power monitoring, and processor extensions such as virtualisation and Turbo Boost.

The BIOS was never designed to be extended ad infinitum in this way. At heart, it’s a 16-bit system, with very limited integration with the hardware and operating system, and it can access a maximum of only 1MB of memory. It’s becoming increasingly difficult to accommodate everything we expect from a modern computer within the old BIOS framework. A new approach is needed.

The UEFI approach

Enter UEFI, the Unified Extensible Firmware Interface. UEFI is a much more sophisticated approach to low-level system management. You can think of it as a miniature operating system that sits on top of the motherboard’s firmware, rather than being squeezed inside it like a PC BIOS. It’s therefore debatable whether or not it’s really meaningful to talk about a “UEFI BIOS” (see What’s in a name?, below).

A modern UEFI BIOS lets you control low-level hardware settings via a graphical, mouse-driven interface

This means that UEFI can be just as powerful as a “real” OS. It can access all the memory installed in a system, and make use of its own little disk storage space – a sequestered area of onboard flash storage or hard disk space called the EFI System Partition. New modules can be easily added (hence “Extensible”); this includes device drivers for motherboard components and external peripherals, so user options can be presented in an attractive graphical front-end, controlled with the mouse. On touchscreen hardware, it’s possible to change system settings by swiping and tapping. It’s all a far cry from the clunky blue configuration screen of most BIOS implementations.

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