What is a boot disk (startup disk) and why would I need one?
A boot disk (sometimes called a startup disk) is a type of removable media, such as a floppy disk or a CD, that contains startup files that your computer can use to start Windows. The startup files are also stored on your computer's hard disk, but if those startup files become damaged, you can use the files on a boot disk to start Windows.
In earlier operating systems that used the FAT or FAT32 file systems, such as Windows 95 and Windows 98, a boot disk was especially useful because it allowed a person to access files on a hard disk even if Windows was unable to start. This ability also represented a security risk, because anyone with a boot disk and access to the computer could start the computer and access any file. Hard disks formatted with NTFS have built-in security features that prevent using a boot disk to access files.
The Windows installation disc contains the files necessary to start Windows, so it is itself a boot disk. If a problem is preventing Windows from starting, you can use the installation CD to start Windows. The installation CD also contains Startup Repair, which you can use to repair Windows if a problem prevents it from starting correctly. Startup Repair can automatically fix many of the problems that in the past required a boot disk to fix.