IBM 3274 51C Maintenance Information page 247

F.1 Introduction
F.l.l General Description
The IBM 51TD Diskette Drive is a direct·access, read/write,
data storage device. This drive uses the flexible magetic
diskette for data entry, data exchange, and data storage.
1'1;i'e
Sr1i'l) \Yi!.'r,"C·"L"~ 'Ui;I'('e, -:.'o,i:,'ll("r1 ;Ii'l r:;,~.!~~ ~", ~~'i1l !I'~,G!'j,
from and write on one side of a diskette 1 and either side
of a diskette 2.
F.1.1.1 Diskette Description
The IBM 51 TD Diskette, shown in Figure F-2, is a thin,
flexible disk, permanently protected in a jacket. I nforma·
tion is stored magnetically on the diskette surface, which
is covered with magnetic recording material. The diskette
is free to turn inside the jacket. As the diskette turns, the
inner surface of the jacket cleans the diskette.
The diskette jacket has three holes. The first hole permits
the diskette driv'e to turn the diskette, the second hole per·
mits the read/write head to make contact with the diskette,
and the third hole permits the phototransistor light to go
through the index hole to sense the type of diskette. For,
storage, the diskette, which is permanently protected in a
thin jacket, can be placed in an envelope. Data can be read
from or written_on either side of the diskette.
Information is written on the diskette in tracks. A track is
a circular path on the diskette surface. Information is mag·
netically written on or read from a track by a read/write
head as the diskette turns. See Figure F-2.
Fi$Jure F-1. IBM 51TO Diskette Drive
P-2
IBM
Dlske
Access Hole for
Index Sensing
Access Hole for
Rotating the Diskette
- - . J l - - - - -
Access Hole for
Read/Write Head Contact
Diskette
Sector
_-'--'. -......... Side 1 }
._/.------- .••
-----~
Track 00 Cyiinder 0
,/ _ . Side 0
--1-- Track 00
Side 1 }
Track 76 Cylinder 76
Side 0
Track 76
-------
_
..
"
--
---
....
---
--
--
--------"",.,
Figure F-2. 51 TO Diskette
There are 77 tracks on each side of a diskette. Track 00,
which is the outside track, is reserved as a label track and
cannot be used for data. Tracks 75 and 76, the two tracks
nearest the hub, are reserved as alternative tracks and can
be used for data only if another track becomes damaged.
A total of 74 tracks on one side of a diskette 1 and on each
side of a diskette 2 and 2D are available for recording data.
A se,ctor is that part of a track used for one record of
information.
A cylinder is defined as the tracks of a diskette that can be
read from or written on without moving the read/write
heads.
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