The boot sector is the area on a hard disk and floppy disks containing instructions that are executed during the boot process, i.e. when the PC starts. Among other things, the boot sector specifies the location of the operating system files. On a hard disk, the boot sector is the first sector(s) on the bootable partition, i.e. the partition containing the system files. On a floppy disk, the boot sector is the first sector on the disk: all floppy disks contain a boot sector, even if they are just data disks.