First, you will need a bootable CD. This has a special "boot" sector: it tells the computer where the operating system is. If you want to boot a Linux-based operating system, you probably downloaded an image format, typically an ISO. This is an exact copy of the disk image, including the boot sector. This file will need to be copied by a program that supports these image files; simply copying and pasting the ISO to the CD won't work. Windows installation CDs come formatted with the boot sector.
When you turn on your PC, it's started by the BIOS, a memory chip that tells the computer where all the basic hardware is. Among other things, it decides which device the computer should use to load the operating system. Most of the time you'll be loading the OS from the hard drive, so most computers are set to look there first to speed up boot time.
To boot off a CD, you'll need to change this boot order. When you turn on the computer, you'll see a short text message saying something like "Press (key) to access setup." Press this key, typically Delete or F10, repeatedly until the boot menu comes up. Sometimes you may miss it: you'll need to restart the computer and continually press this key until the boot menu loads. There will be a "Boot" option that will list the order of devices the computer boots from. Move the CD drive to the top of the list, save the setting, and reboot.
Some newer computers give you a choice of the BIOS menu or a special boot menu.
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At the boot menu you can choose where you want to boot for this one time, so you won't have to change back to booting from the hard drive the next time you use the computer.
Posted 3598 day ago