1 02 Macintosh
User's
Handbook
disks are structured by placing data in magnetic form following
a series
of
concentric circles around the disk. These circles are
called tracks and act much like the tracks around a phono-
graph record. The Mac's disks can hold
80
tpi (tracks per inch)
as opposed to the
70
tpi for the standard Sony
3~
inch
diskettes.
When loading data on a disk, most disk drives use one
rotation speed and one
data
rate. Each track on the disk
is
divided into sectors each containing
512
characters. Since the
rotation speed and the data rate are constant, the sectors near
the edge
of
the disk are longer than those near the center
of
the
disk. This essentially wastes disk space.
The Macintosh disk drive
is
designed to operate
at
varia-
ble speeds to allow it to record data on the disk with each sector
having the same length. Rotation speeds range from
390-600
rpm. When operating near the rim
of
the disk, the drive turns
at
a slower speed. When near the center, it rotates faster.
Although this
is
a great help for the Mac in terms of data
storage efficiency, it has the disadvantage that no other compu-
ter, with the exception
of
the Apple Lisa, can read the Mac's
disks. Likewise, the Mac
(or
the Lisa) cannot read disks
recorded on most other computer systems.
Since the Mac's drives have been extensively tested and
since they require
few
adjustments, the disk drive should oper-
ate for an extended period
of
time without the need for repair.
Disk ejection
is
under the control
of
the Mac's software.
Most other floppy disk drives allow the operator to remove the
disk
at
any time. Placing the disk ejection under the Mac's
control insures
that
the Mac
will
have the opportunity to
update the disk before it
is
removed. Such updating might
include Trash file removal, storage
of
display formatting, and
proper file closure.
In this chapter,
we
will outline the commonly used disk
operations required when working with the Mac. Although
we
will make reference to the applications available on the Mac,
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