RANA Systems Elite Controller, Руководство пользователя

Страница: 276 / 328

ELITE SERIES USER MANUAL APPEN. A - DISK I/O
The disk ann can physically position itself over
80 “phases”. To move an Elite One or Two past
one track (cylinder) to the next, two phases of
the stepper motor, which moves the arm, must be
cycled. This would suggest that data might be
stored on 80 tracks, but only the Elite Three is
equipped with heads which are capable of reading
and writing data on tracks which are so close
together. For the Elite One and Elite Two (and
Disk II) the resolution of the read/write heads
are such that attempts to use “half—tracks”
often invite complications.
A sector, a sub—division of a track, is the
smallest unit of “updateable” data on the disk-
ette and Apple has used two different track
formats to date. One divides the track into 13
sectors, the other into 16 sectors. The sect or—
ing does not use the index hole(s) provided on
most diskettes to locate the first sector of the
track. In stead DOS uses an extended “soft sec-
toring” format which takes up more space but,
ultimately allows more flexibility, and reduces
drive costs.
Since the existing Apple II operating systems
(DOS, CP/M, and Pascal) knew nothing of dual
headed disk drives like the Elite Two and Elite
Three, special (but very compatible) extensions
to Apple’s diskette format had to be made to
support these higher capacity drives. This was
done by leaving the format on the first side of
the diskette identical to Apple’s, but numbering
the sectors on the second side of the diskette
as sectors 16-31.
P a g e A - 5