Basic Input/Output System

What Does Basic Input/Output System Mean?

A basic input/output system (BIOS) is a preinstalled program used during startup on Windows-based computers. The CPU initially accesses the BIOS, after which the operating system is loaded.


A basic input/output system is also known as system BIOS or ROM BIOS.

Techopedia Explains Basic Input/Output System

The BIOS is built-in software that contains generic code required to control the keyboard, display screens, disk drives and other functions. The primary purpose of the BIOS is to set up hardware and further load and start an operating system. BIOS is placed in a nonvolatile ROM chip inside the computer, ensuring the availability of BIOS at all times and preventing accidental disk failure. The BIOS checks every hardware connection and locates the devices, after which the operating system is loaded into computer memory.

BIOS software is designed to work with the various devices that make up a complimentary system chipset. The BIOS library has certain functions used to operate and control system peripherals, which can be initiated by an external software.

Users using the BIOS user interface can perform functions such as:

  • Setting the system clock
  • Enabling and disabling certain system components
  • Hardware configuration
  • Selecting boot drives
  • Set password prompts for secured access to BIOS user interface function

Modern PCs have BIOS stored in rewritable memory, permitting contents to be rewritten or replaced. Such content rewriting is called flashing and is executed through a special program provided by system manufacturers.


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Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.