A BIOS is the small, built-in program that runs the moment you power on a computer, before the operating system loads. Its job is to check that the essential hardware is present and working, then find a drive to start the operating system from and hand control over to it. The name stands for Basic Input/Output System, and it lives on a chip on the motherboard so it is always available. On modern PCs the BIOS has been replaced by a newer version called UEFI, though people still casually call it the BIOS. Here is how it works and when you would ever open it.
What the BIOS does at startup
When you press the power button, your computer cannot run an operating system yet, because that software lives on a drive it has not read. The BIOS bridges that gap. In a fraction of a second it performs a quick self-test of core components like memory and storage, applies basic settings such as the system clock and boot order, then locates a bootable drive and starts loading the operating system. After that hand-off, the operating system takes over and the BIOS steps back.
Think of it as the building superintendent who unlocks the doors, flips on the lights, and confirms everything is safe before the staff arrive to do the actual work. The chip that does this lives on the motherboard, the board that connects every other part of your computer.
BIOS vs UEFI
Most computers sold today use UEFI, a modern firmware that does the same fundamental job as the original BIOS but with more capability. The two names are often used interchangeably in everyday speech.
| Aspect |
Classic BIOS |
UEFI |
| Age |
Older standard |
Modern standard |
| Interface |
Text-only, keyboard |
Often graphical, mouse support |
| Boot drive size |
Limited |
Supports very large drives |
| Security features |
Minimal |
More, including secure boot |
| Common name today |
Still called BIOS |
Often still called BIOS |
The practical takeaway: if your PC is reasonably modern, you are almost certainly using UEFI even if the screen and menus still say BIOS.
Why you would ever open it
Most people never need to enter the BIOS, but a few situations call for it. You usually access it by pressing a specific key right after powering on, such as a function key or Delete, shown briefly on the startup screen.
- Changing the boot order, for example to start from a USB drive when installing or repairing an operating system.
- Fixing the date and time if the system clock keeps drifting.
- Enabling or disabling a hardware feature, such as a virtualization setting or a security option a program requires.
- Checking hardware the system detects, like installed memory or storage, when troubleshooting.
Common misconceptions
- The BIOS is the operating system. It is not; it only starts the operating system, then steps aside.
- You should tweak it for speed. For most users, default settings are correct; random changes risk a system that will not boot.
- BIOS and UEFI are completely different things. UEFI is the modern evolution of the BIOS and serves the same core purpose.
- Updating the BIOS is routine. Firmware updates can help, but they carry risk, so only update with a clear reason and the correct file.
FAQ
What does BIOS stand for?
Basic Input/Output System. It is the firmware that initializes hardware and starts the operating system when you turn on the computer.
How do I get into the BIOS?
Press the key shown on the startup screen immediately after powering on, often a function key or Delete. The exact key depends on your computer maker.
Is UEFI the same as BIOS?
UEFI is the modern replacement for the classic BIOS. It does the same core job with more features, and people still commonly call it the BIOS.
Should I update my BIOS?
Only with a specific reason, such as fixing a known issue or supporting new hardware. Use the exact file for your model and avoid interrupting the process.
Where to go next
Learn the brain it starts in What Is a CPU in 2026, understand the boot drive in What Is a Solid State Drive in 2026, and see what keeps drivers current in How to Update Your Drivers in 2026.