PC Hardware A Beginner’s Guide

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Chapter 9: Hard Disks and Floppy Disks^199


Seek times on a floppy disk are relatively slower than on a hard disk. It is common
that the seek time associated with moving the read/write head from the innermost track
to the outermost track on the disk requires 200 or more milliseconds.


Spindle Motor


When the floppy disk is inserted into the drive, clamps attached to the spindle motor
clamp the disk into place. The spindle motor then rotates the disk so that the media
moves under the read/write heads. The speed of the spindle motor is tied to the physical
size of the disk, but for the 3.5-inch disk, the spindle motor rotates the disk at 300 rpm.
This very slow rotation speed adds to the latency and data transfer speeds of the disk, but
it also keeps the contact heads from wearing out the disk.


Connectors


A floppy disk drive connects to the system through two connectors. The data connector is
used to connect the floppy disk to the floppy disk controller. Typically, the data cable
connects either one or two floppy disk drives. On systems that connect two floppy disk
drives (extremely rare on newer systems), the cable is used to connect one drive as the A
drive and another as the B drive.
The other floppy disk connector is used to connect the disk drive to the power supply.
This connector will be either a very similar connector to the one on the hard disk drive or
a much smaller connector that should have a mate coming from the power supply on
nearly all power supply form factors.


Media


The first floppy disks were eight inches, but the first ones to gain widespread use on the
PC were 5.25 inches, still large when compared with today’s popular 3.5-inch size. A
5.25-inch disk, shown in Figure 9-11, has primary components: the flexible round piece of
magnetic oxide coated plastic media and the outside somewhat rigid plastic jacket.
The 5.25-inch disk has a large center hole used to clam pthe disk to the s pindle so it can be
rotated. The outside jacket does not turn; the disk is rotated inside of it. The read/write
head contacts the disk through the read/write slot that is long enough to allow the head
to reach all of the tracks on the disk. In an effort to prevent the disk from being written to
accidentallyandoverwritingsomeimportantdata,thewrite-protectionnotchcanbecov-
ered to disable the write function.
The 3.5-inch disk was developed to overcome the fragility of the 5.25-inch disk and to
provide a smaller, more protected disk. The 3.5-inch diskette added a sturdier packaging, a
metalslidetoprotecttheread/writeslotandaslidingswitchforwrite-protectionofthedisk.
Both the 5.25-inch and the 3.5-inch disks have had different data density standards
over the years. Usually the density was given a name that generally described how dense
the disk actually was. The density standards have gotten increasingly higher, from the
original single-density disks, which had a bit density of around 2,500 bpi and 24 tracks

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