Flash and Removable Storage - Upgrading and Repairing PCs - page 643

tp://physics.nist.gov/cuu/Units/binary.html . Also, refer to the section “ Capacity Measure-
ments ” in Chapter 8 .
Like blank sheets of paper, new, unformatted disks contain no information. Formatting a
disk is similar to adding lines to the paper so you can write straight across. Formatting the
diskwritestheinformationtheOSneedstomaintain adirectoryandfiletableofcontents.
Afullformatrewritesthefilesystemstructures,removinganyexistingdataintheprocess.
This is the equivalent of both a high-level and low-level format on a hard disk. However,
unlike a hard disk, a floppy disk does not need to be partitioned.
Note
The Quick Format option available in most versions of Windows erases the contents of the
diskandverifiesthefilesystemratherthanrewritingthefilesystem.Ifyourun FORMAT.EXE
from the command line, the /Q option also performs a quick format. Unfortunately, Quick
Format is not very good at determining whether you have problems with your floppy disk's
file system. If you need to ensure that the floppy disk is properly formatted (such as in the
case of a used disk you want to use for another task), you should not use the Quick Format
option. Windows normally performs a full (low-level) format that rewrites the file system
and clears the disk if Quick Format is not selected.
When you format a floppy disk, the OS reserves the track nearest to the outside edge of
a disk (track 0) almost entirely for its purposes. Track 0, Side 0, Sector 1 contains the
volume boot record (VBR), or boot sector, that the system needs to begin operation. The
next few sectors contain the file allocation tables (FATs), which keep records of which
clusters or allocation units on the disk contain file information and which are empty. Fin-
ally, the next few sectors contain the root directory, in which the OS stores information
about the names and starting locations of the files on the disk.
Note that floppy disks have been sold in preformatted form for a few years now. This
saves time because the formatting can take a minute or more per disk. Even if disks come
preformatted, they can always be reformatted later. This is useful if you accidentally pur-
chased Mac-formatted disks for your PC; a PC can't use a Mac-formatted floppy disk un-
less you reformat it.
Disk Change
The standard PC floppy controller and drive use a special signal on pin 34 called Disk
Change (DC) todeterminewhetherthediskhasbeenchanged—ormoreaccurately,tode-
termine whether the same disk loaded during the previous disk access is still in the drive.
DCisapulsedsignalthatchangesastatusregisterinthecontrollertoletthesystemknow