Theory; Introduction; Diskette Description - IBM 5280 Maintenance Information Manual

INTRODUCTION
The diskette drives used with the IBM 5280 system are
input/output (I/O) devices that rely upon the unit in which
they reside for power and some signals. The diskette drive
stores and retrieves data by writing data on diskettes for
later use and by reading data from diskettes for immediate
use. The commands and controls needed for operating the
diskette drives are provided by the system. The IBM 5280
system uses two types of diskette drives: 31SD and 51TD.
The 31 SD diskette drive can read from and write on a
diskette 1. The 31 SD diskette drives write and read only
in FM (frequency modulntion). If a diskette 2 or a diskette
2D is inserted into a 31SD diskette drive, the diskette drive
will not come ready.
The 51 TD diskette drive can read from and write on
diskettes 1, 2, and 2D. The 51 TD diskette drive can read
and write in both FM and M FM (modified frequency
modulation).
DISKETTE DESCRIPTION
The IBM diskette is a thin, flexible disk, housed in a
protective envelope. Information is stored magnetically
on the diskette surface, which is coated with magnetic
oxide. The diskette is free to turn inside the envelope. As
the diskette turns, the inner surface of the envelope cleans
the diskette. The envelope has access holes for turning the
diskette, for read/write head contact, and for index sensing.
Data can be read from or written on both sides of a diskette
2 and a diskette 2D and one side of a diskette 1.
Access Hole for
L3:=
Index Sensing
• Access Hole for
o
I
Rotating the Diskette
~
___ - Access Hole for
1-
Read/Write Head Contact
D
Theory
The location of the index hole on the diskette 1 differs
from that on a diskette 2 and diskette 2D. When a diskette
1 is inserted into a diskette drive, index sensing circuits
sense that a diskette 1 is being used and the use of the
blank side is prevented.
IBM
DI.k.~~
Diskette 1
IBM
DI.k ..........
~
Diskette 2
Theory 59