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4.2
POSITIONING CHARACTERISTICS
Head positioning is governed by five timing characteristics:
A.
Time for a single-track move is 25 milliseconds. This is the time
required to move the R/W head between any two adjacent tracks.
B.
Head settling time is 15 milliseconds. This is the time required for
the head assembly to cease oscillating after the head has achieved
nominal track location following a move.
C.
Random average access time (T) is 298 milliseconds (35 tracks) or
340 milliseconds (40 tracks). This time is determined from the
following equation:
(No. of tracks - 1) (Step time)
T
=
+
Settle Time
3
D.
The time to move the R/W head 39 tracks is 975 milliseconds. It
is defined as the time to move the head from track 00 to track 39,
or from track 39 to track 00.
E.
Head load time is 50 milliseconds. This is the time required for the
head load arm to contact the diskette and settle down before a
Read or Write operation begins.
4.3
DATA FORMAT
To perform data transfer, the operating system must be able to locate specific data areas on the
diskette. Two such format schemes exist; both involve detecting and establishing a reference point
on the diskette to organize data on a track and further divide this track into smaller segments
called sectors. Such a subdivision can be achieved by either hard or soft sector formats. All disk
drive tolerances have been taken into account in developing the formats.
4.3.1
HARD SECTOR FORMAT
The controller will typically record 10 or 16 sectors (records) per track due to the availability of
hard-sectored diskettes in these configurations. Each track is started by an Index pulse, and each
sector is started by a Sector pulse which is present on connector pin J1-8. Figure 4-2 shows a
hard-sectored format. The number of sectors is determined by the number of sector holes in the
diskette.
4-5
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