Hardware Reference
In-Depth Information
use floppy drives much for storing new information, I maintain systems with both 5
1/4-inch and31/2-inch drives soIcan read data fromolder floppymedia inaforensics or
data-recovery situation.
1.44MB 3 1/2-Inch Drives
The 3 1/2-inch, 1.44MB, high-density (HD) drives first appeared from IBM in the PS/2
product line introduced in 1987. Most other computer vendors started offering the drives
as an option in their systems immediately afterward. For systems that include floppy
drives, the 1.44MB type is still by far the most popular.
The drive records 80 cylinders consisting of two tracks each with 18 sectors per track,
resulting in a formatted capacity of 1.44MB. Some disk manufacturers label these disks
as 2.0MB, and the difference between this unformatted capacity and the formatted usable
result is lost during the format. Note that the 1440KB of total formatted capacity does
not account for the areas the FAT file system reserves for file management, leaving only
1,423.5KB of actual file-storage area.
The drive spins at 300 rpm and in fact must spin at that speed to operate properly with ex-
isting high-andlow-density controllers. Tousethe 500KHzdata rate (the maximum from
most standard high- and low-density floppy controllers), these drives must spin at a max-
imum of 300 rpm. If the drives were to spin at the faster 360 rpm rate of the 5 1/4-inch
drives, they would have to reduce the total number of sectors per track to 15; otherwise,
thecontrollercouldnotkeepup.Inshort,the1.44MB31/2-inchdrivesstore1.2timesthe
data of the 5 1/4-inch 1.2MB drives, and the 1.2MB drives spin exactly 1.2 times faster
than the 1.44MB drives. The data rates used by both of these HD drives are identical and
compatible with the same controllers. In fact, because these 3 1/2-inch HD drives can run
at the 500KHz data rate, a controller that can support a 1.2MB 5 1/4-inch drive can also
support the 1.44MB drives.
Other types of floppy drives that have been used in the past include the following:
•
2.88MB 3 1/2-inch
—This size was used on some IBM PS/2 and ThinkPad models in
the early 1990s.
•
720KB 3 1/2-inch
—This size was used by IBM and others starting in 1986 before the
1.44MB 3 1/2-inch drive was introduced.
•
1.2MB 5 1/4-inch
—This was introduced by IBM for the IBM AT in 1984 and widely
used throughout the rest of the decade.
•
360KB 5 1/4-inch
—An improved version of the floppy disk drive originally used by
the IBM PC, it was used throughout the 1980s on XT-class machines and some AT-
class machines.
