BOOTING of Computer

BOOTING


Boot means 'start' or make the computer system ready for taking instructions. The word "boot" comes from "bootstrap," since bootstraps help you to get your boots on; likewise, booting the computer helps it to get its (ROM) instructions loaded in its main memory. When the computer is first switched on, it is called cold booting. When the computer is already ON and is being reset, it is called warm booting.


When you turn your computer on, chances are that the operat ing system has been set up to boot. It follows the below sequenc


1. As soon as the computer is turned on, the Basic Input/Output System (BIOS) on your system's ROM chip is "woken up" and takes charge. BIOS is already loaded because it is built into the ROM chip and, unlike random access memory, ROM contents do not get erased when the computer is turned off.


2. BIOS first does a "Power-on Self Test" (POST) to make sure all the computer's components are operational. Next, the BIOS's boot program looks for the special boot programs that will actually load the operating system onto the hard di k.f.e:g.rd disk.


3. First, it looks on drive A (unless you have set it up some other way or there is no diskette drive), at a specific place where operating system boot files are located. (If the operating sys tem is MS-DOS, for example, it will find two files named IO.SYS and MSDOS.SYS). If there is a diskette in drive A but it is not a system disk, BIOS will show a message that drive A does not contain a system disk. If there is no diskette in drive A (which is the most common case), BIOS looks for the sys tem files at a specific place on your hard drive.


4. Having identified the drive where boot files are located, BIOS next looks at the first sector (a 512-byte area) and copies information from it into specific locations in RAM. This information is known as the boot record or Master Boot Record.


5. It then loads the boot record in RAM. 6. The boot record contains a program that BIOS now branches


to, giving the boot record control of the computer. 7. The boot record loads the initial system file into RAM from the diskette or hard disk.


8. The initial file then loads the rest of the operating system into RAM. (At this point, the boot record is no longer needed and can be overlaid by other data).


9. The initial file loads a system file (for example, MSDOS.SYS) that knows how to work with the BIOS.


10. One of the first operating system files that is loaded is a sys tem configuration file. Information in the configuration file tells the loading program which specific operating system files need to be loaded (for example, specific device driver).


11. Another special file that is loaded is one that tells which spe cific applications or commands the user wants to have included or performed as part of the boot process. In DOS, this file is named AUTOEXEC.BAT. In Windows, it is called WIN.INI.


12. After all the files have been loaded, the operating system is given control of the computer and performs requested initial commands and then waits for the first interactive user input.


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