Modern operating systems and application program code and data are stored on nonvolatile data storage devices, such as hard disk drives, CD, DVD, flash memory cards (like an SD card), USB flash drive, and floppy disk. Ī computer's central processor can only execute program code found in Read-Only Memory (ROM), Random Access Memory (RAM) or an operator's console. Then the computer initializes the BIOS variables and the interrupt vector table. Īfter determining the function of the main board, the computer tests the peripherals (keyboard, disk drive, etc.). Each chip on the main board goes through tests and initialization. If the CPU passes the test, BIOS tests the ROMs by computing checksum. If an error occurs during this test, the system stops without displaying an error message. įirst the BIOS tests individual functions of the processor, its register and some instructions. The location of this routine may differ from one computer to another, however the task this routine performs remains identical for nearly all PCs. This is part of the ROM-BIOS and contains a jump command to a BIOS routine which takes over system initialization. Program execution starts after the computer is turned on at memory location F000:FFF0. This process is known as booting, or booting up, which is short for bootstrapping. The BIOS then locates software held on a peripheral device (designated as a 'boot device'), such as a hard disk or a CD, and loads and executes that software, giving it control of the PC. When the PC starts up, the first job for the BIOS is to initialize and identify system devices such as the video display card, keyboard and mouse, hard disk, CD/DVD drive and other hardware. The primary function of the BIOS is to load and start an operating system. The BIOS of a PC software is built into the PC, and is the first code run by a PC when powered on ('boot firmware'). In Windows, when the pointer goes from the hour glass to the normal pointer, the operating system has been loaded and all the subsystems are synchronized and ready for user requests to process data.
From the time we switch on the computer to the booting process, a series of the following events occur. The booting process of DOS begins with the examination of the first sector of a diskette or hard disk is loaded into memory. For example, Macs allow users to run OS X, Windows, and Linux using the Boot Camp boot manager that comes as a OS X utility. This allows for multiple boots to allow different operating systems to be loaded and used on the same computer.
Learning objective: Describe the events of the booting sequenceĮvery time you turn on your computer, its as if its the first time your computer has ever been turned on since there are no instructions or data in memory. Operating Systems Architecture Operating Systems Architecture
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