Question #4575

the calculated capacity of floopy disk to store is 1.47 mb while the actual capacity is 1.44mb the differnece is 0.03 where the floppy disk use the capacity

Expert's answer

Floppy disks often have two capacity specifications; they are often

quoted with both their unformatted capacity, and their formatted

capacity. Since the disk is useless unless it is formatted the

unformatted capacity means basically nothing. The formatted capacity is

the true maximum capacity of the disk. Usually, the formatted capacity

is about three-quarters the unformatted capacity.

Even the formatted capacity, however, doesn't show the true amount of

space available for user files, because a certain amount of overhead is

taken up for FAT file structures. This is true of hard disks as well, of

course, although as a percentage more of the floppy is taken up by this

information than a hard disk is. The amount of space remaining after

these structures are placed on the disk is the true usable capacity of

the floppy.

Note also that the "decimal vs. binary" measurements problem is in play

again with the terminology used to specify floppy capacity. In fact, the

terms are not even consistent in and of themselves. For example, a 1.44

MB floppy disk takes its name from the fact that the disk has 2,880

sectors, and each sector is 0.5 KB; 0.5 times 2,880 is 1,440, so the

1.44 is a decimal measure. But, each sector is really 512 bytes, so the

0.5 KB is a*binary* measure. As a result the "1.44" is a mixed measurement; the true raw formatted capacity is either 1.41 MB (binary)

or 1.47 MB (decimal), and not 1.44 MB at all

quoted with both their unformatted capacity, and their formatted

capacity. Since the disk is useless unless it is formatted the

unformatted capacity means basically nothing. The formatted capacity is

the true maximum capacity of the disk. Usually, the formatted capacity

is about three-quarters the unformatted capacity.

Even the formatted capacity, however, doesn't show the true amount of

space available for user files, because a certain amount of overhead is

taken up for FAT file structures. This is true of hard disks as well, of

course, although as a percentage more of the floppy is taken up by this

information than a hard disk is. The amount of space remaining after

these structures are placed on the disk is the true usable capacity of

the floppy.

Note also that the "decimal vs. binary" measurements problem is in play

again with the terminology used to specify floppy capacity. In fact, the

terms are not even consistent in and of themselves. For example, a 1.44

MB floppy disk takes its name from the fact that the disk has 2,880

sectors, and each sector is 0.5 KB; 0.5 times 2,880 is 1,440, so the

1.44 is a decimal measure. But, each sector is really 512 bytes, so the

0.5 KB is a

or 1.47 MB (decimal), and not 1.44 MB at all

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