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2.1.11 Disk Description
Data Tracks
Data heads record the data on (and read the data
from) the data tracks. Each track is divided into
60 sectors. The data stored in one sector is called
a record. Each record consists of 256 bytes; there-
fore, it is possible to store 15,360 bytes per track.
The tracks that can be read without moving the
actuator are called a cylinder. Cylinder 0 is the
cylinder toward the center of the disk. Each
track is divided into 60 sectors. The data stored
in one sector is called a record. Each record
consists of 256 bytes; therefore, it is possible to
store 15,360 bytes per track.
The capacities of the various models are shown
in the following chart:
Disk Capacity in Megabytes
3.2
I
5.0 , 9.1
13.7
Number of Tracks
218
J
338
I
606
909
Data Heads-
Tracks per Cylinder
2
3
Bytes per Sector/Record
256
Sectors/Records per Track
60
Because the disk is formatted into cylinders and
sectors, each record on the disk has a definite
address consisting of cylinder, head, and sector
numbers. This address (part of the identification
field) is recorded at the physical location of the
record on the disk.
Some areas of the disk reserved; are shown in the
Diagnostic Service User's Guide.
Cross Section of Disk
Behind Home
Servo Tracks
The servo tracks of the disk contain prewritten
patterns on the outer half of the disk. These pat-
terns correspond to each data track location and
consist of missing clock pulses and position pulses
in a specific sequence. The clock pulses, every
2.1
MS,
develop the 140 ns write clock pulses in
the attachment. The position pulses keep the data
heads over the specified track
(Servo Track Fo/-
lowing,
2.1.19).
Specific combinations of clock and position pulses
define either the beginning of a track (index pulse
that indicates sector 00) or the beginning of
sectors 01 through 59 (sector pulse).
The servo tracks are used by the servo head to
keep the data heads on track and to perform
seek operations.
Data Tracks
Data Tracks
- . - - - --+--t----t--D-a-ta T.:..ra::..c:....:k..:..:s--ll---l---II-----
*13.7 megabyte files only.
2-4
2.1.12 Landing Zone (LZ)
Because the heads touch the disk when it slows to
less than 400 rpm, the heads are retracted to a
landing zone to avoid destruction of data. No
information is written in the landing zone.
2.1.13 Guard Band· (GB)
Between the servo tracks and the landing zone is
the guard band. The guard band is a servo track
area that contains clock and position pulses but
no prewritten patterns. When the servo head is
in the guard band position, the data heads are
behind home (BH).
Data Head 0
Data Head 1
Data Head 2 *
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