Theory Of Operation; Introduction; Addressing Structure; Addressing Structure Of An Hp 7925 Disc Drive - HP 7925D Service Manual

THEORY OF OPERATION
·I~
1-1. INTRODUCTION
This section contains the theory of operation for the disc
drive. Included are a description of its addressing struc-
ture and modes, its sector format, and a detailed discus-
sion of each of its functional systems.
1-2. ADDRESSING STRUCTURE
The disc pack used with this disc drive is comprised of
seven discs. The top and bottom discs provide physical
protection for the five center discs. These five center discs
provide nine data surfaces and one servo surface. As
shown in figure 1-1, the disc drive accesses data on the
nine data surfaces with nine read/write or data heads.
Head positioning information and sector clocking are de-
rived from the fifth (servo) surface through a read only or
servo head. There are 815 ensured cylinder positions
available for data storage. Cylinder addresses range from
zero to 822. Each data cylinder consists of nine data
tracks, one on each data surface. Tracks are addressed
when both cylinder and head addresses are specified. Each
data track is divided into 64 physical data sectors. Sectors
are addressed when both head and sector addresses are
specified for a given cylinder. Head addresses range from
zero to 8 and sector addresses range from zero to 63.
HEAD~
823 CYLINDERS
PER DRIVE
9 DATA HEADS
1 SERVO HEAD
PER DRIVE
CARRIAGE
ASSEMBLY
o
SERVO
4
6
UPPER AND LOWER
PROTECTIVE DISCS
64 SECTORS
PER TRACK
NOTE: A TRACK IS SELECTED WHEN
A CYLINDER AND A HEAD
ARE SPECIFIED
7311-32
DIRECTION
OF ROTATION
jlTOP VIEWI
Figure 1-1. Addressing Structure of an HP 7925 Disc Drive
1-1