If you leave the floppy in your PC when you power on or boot, you will be infected even though the PC won't successfully boot from that floppy. Each physical hard disk drive has one of these sectors. A single physical disk can be partitioned into one or more logical disks. The single partition sector contains the information that describes both logical disks. If the partition sector is damaged, then DOS may not even recognize that your disk exists.
Numerous viruses plant their code in the partition sector.
Modified August 12, 1998.