Hardware Reference
In-Depth Information
if (x And &H0F)=4 Then Print "3.5"chr$(34)" 1.44 MB"
if (x And &H0F)=5 Then Print "3.5"chr$(34)" 2.88 KB"
print division$
end
Disk drives
Disk drives provide low-cost high-capacity storage for data and programs.
Standard floppy disk drives operate at 300 rpm and use an 80-track format
with 135 tracks per inch. The standard data transfer rate is around 250 KB/s
while the formatted storage capacity is 1.44 MB.
Like floppy disks, the data stored on a hard disk takes the form of a magnetic
pattern stored in the oxide-coated surface of a disk. Unlike floppy disks, hard
disk drives are sealed in order to prevent the ingress of dust, smoke and dirt
particles. This is important since hard disks work to much finer tolerances (track
spacing, etc.) than do floppy drives. Furthermore, the read/write heads of a hard
disk 'fly' above the surface of the disk when the platters arc turning. The speed
of data transfer greatly exceeds that of a floppy disk drive because the hard
disk rotates at speeds of typically between 4200 and 7200 rpm (around 20 times
faster than a floppy drive).
Modern Integrated Drive Electronics (IDE) hard drives are designed to inter-
face very easily with the PC bus by means of one, or more, 40-way IDC
connectors on the motherboard. The 40-way bus extension is sometimes known
as an
AT attachment
(ATA). This system interface is simply a subset of the
original ISA bus signals and it can support up to two IDE drives in a
daisy
chain
fashion (i.e. similar to that used originally with floppy disk drives).
IDE drives are
low-level formatted
with a pattern of tracks and sectors already
in place. This allows drives to be more efficiently formatted than would other-
wise be possible. The actual
physical
layout of the data on the disk is hidden
Photo 1.13
Interior of a hard disk drive
