If you want to run Linux on your computer, first you are going to have to learn how your computer chooses what operating system to run, including how to choose to make it run Linux.
When your computer is powered on, the bios (basic input/output system) takes control of your computer. The relevant fact for us now about the bios is that it decides where to look for software on the computer and what order to look at these places in. Usually computers will look to the hard disc for the software they will run, though often they will also check for a floppy disk, cd/dvd, network connection or flash memory which can be used to start the computer. Usually when you are installing an Operating System on to your computer, you will boot up from an installation cd/dvd to perform the installation, so your bios will need to be setup to check the cd/dvd before the hard disk. If you want to try out a LiveCD version of Linux, you will also need to have your bios setup similarly.
If you are planning on installing Linux or running a LiveCD, you may be lucky and already find that your computer will boot from the cd/dvd drive. There is no harm in trying to put the cd in and then restarting your computer, if it starts up as normal then you will need to check and probably change the bios, if you see some new massages (probably mentioning Linux somewhere) then you can leave the bios alone and continue on to install Linux or try out that cd.
To check or change the setup in your bios, you will need to restart your computer, and press a key to enter the setup function, before it starts to load any operating system. Usually you will need to press F1, F2, Escape or Delete, if there are no messages on the screen to tell you what to press (or if they go to fast to read them) you may have to consult your motherboard or computer manual. Once you enter the bios setup, you should look for instructions on how to use the setup, and ensure you do not save any changes you did not mean to make, as this could prevent your computer from booting up properly. Generally you will be looking for an option called "boot order" or similar and here you should have the chance to ensure the computer will check the cd/dvd drive before the hard disk. If you have to change the boot order, you will need to save your changes before you leave the bios setup (there is usually a "save and exit" option which will ask you to confirm that you want to make the changes). If you are unsure ask a friend to help!
If you are unable to boot from a cd/dvd, perhaps the page Making a boot floppy to start
from will help.
When your bios is starting up the software on your computer, what it actually does is attempt to get a small piece of code, called a boot loader from each place it has been told to look, one at a time, in order. It uses the first copy of the information it finds to start loading software on to the computer. When the bios comes to look at hard disks for a boot loader, it looks at the very start of the disk, a space on the disk called the master boot record or mbr. Unless you have scsi hard disks (and if you don't know what this means assume you don't) then the bios will actually just check for an mbr on the "first" hard disk (the master disk on the first controller to be more precise). If you only have one operating system installed on your computer, all the software in the mbr needs to do is start that system. If you have multiple Operating Systems installed on your hard disk(s) then this mbr needs to offer you a way to choose between them and then start them up. When you are installing Linux, you will usually be given the chance to install grub or lilo as your boot loader, and also the chance to make a boot floppy (to use this your bios would need to check for floppy disks to boot from before the hard disk). Both grub and lilo will happily start other operating systems, and many Linux distributions will set this up automatically and so the recommended approach is to install one of these into the mbr. Alternatively you can install lilo or grub to the same partition as Linux (and NOT the mbr) and make the Windows NT/2000/XP boot loader offer a choice to start Linux. Finally on Windows 95/8 you can use loadlin to start Linux from dos.
Always remember that if your computer is set to boot first from a removable device (cd/dvd or floppy) then it will always boot from this device if it can, so you will normally want to ensure there is no bootable disk in the drive when you start the computer. When you are finished installing Linux, or using a LiveCD, you should remove the cd/dvd from the drive before restarting your computer, letting your system boot up normally from the hard disk. Keep the disk safe though as in the event of a problem with your computer, you know have a rescue disk you can use to boot up and fix problems.
Dual Booting Linux and Windows
About the author, Niall Walsh.