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1. .GENERAL DESCRIPTION
INTRODUCTION
The Xerox Model 7260/7261/7264 and Model 7265/7266/
7264 Removable Disk Storage Systems provide high-volume,
random-access storage.
Each is a moving-arm (head),
removable-medium, rotating disk system available for use
as secondary storage with Sigma 5-9 computers. The two
systems provide greater capacity and performance than the
Xerox Model 7240/7242/7246 Removable Disk Storage
System.
Model 7260 comprises a controller and two 45 million-byte
disk drives, providing a starter capacity of 90 mill ion bytes
of storage. A maximum of 13 Model 7261 disk drives ("A"
drives), each providing 45 mil lion bytes, can be added to
the system to allow a total on-line capacity of 675 million
bytes per control I er. The opti~nal addition of one Model 1032
controller, and a Model 1033 dual access feature for each
drive provides dual access to the system (see Chapter 4,
"Dual Access Considerations"). The Model 7264 disk pack,
an 11-high, 20 surface disk pack is the removable storage
medium.
The Model 7265/7266/7264 system is designed for appli-
cations requiring large on-line storage capacity.
The
Model 7265 comprises a controller and three 91 million-
byte disk drives, providing a starter capacity of 273 mil-
l ion bytes. A maximum of 12 Model 7266 disk drives ("B"
drives), each providing 91 million bytes of storage, can be
added to the system to allow a total on-line capacity of
1365 million (1 billion, 365 million) bytes of storage.
Dual access is made possible by adding one Model 1034
controller, and a Model 1035 dual access feature for
each 7266 disk drive. The removable storage medium is
the Model 7264 disk pack.
To use this manual effectively, the reader must be famil-
iar with the applicable Xerox Sigma Computer Reference
Mani.Jal, particularly the discussions of input/output instruc-
tions and input/output operations.
The particular features of the two removable disk systems
include the following:
1.
Floating
I
inear actuator - isolates carriage movement
reaction forces from the cabinet structure.
2.
Electromagnetic head .positioner - provides an average
30 msec cylinder access time.
3.
Electro-optical tracking - optimizes head positioning
precision.
4.
Thermal compensation - minimizes off-track errors
caused by temperature changes.
5.
Operation and failure interlock system - assures oper-
ational system integrity.
6.
Dual access (optional)-allows simultaneous read/read,
read/write, or write/write on any two spindles in a
set of 15.
7.
Hardware write-protect - assures total file protection
of the entire spindle.
8.
Independent Seek operations - allows overlapping of
Seek operations to minimize access times on multiple
spindle systems.
The added feature of the 7265/7266 system is, of course,
an on-line file storage capacity of 1365 million bytes
per control I er.
SYSTEM COMPONENTS
The "A" system (7260/7261) comprises some combination
of the following components:
Model
No.
Component
7260
Disk controller with two 45million-
byte disk drive units.
1032
Additional controller allowing
access of 7260/7261 disk drives,
if dual access feature 1033 is
installed (optional).
1033
Dual access feature - one re-
quired for each 7260/7261 disk
drive (optional).
7261
Additional 45-million-byte disk
drive unit- maximum of 13 per
7260 controller (optional).
7264
Removable disk pack.
Prerequisite
Component
7260
1033
7260/7261
7260
The minimum configuration is one Model 7260 disk system
(controller and two 45 million-byte disk drive units).
Similarly, the "B" system (7265/7266) comprises some com-
bination of the fol lowing components:
Model
No.
Component
Prerequisite
Component
7265
1034
Disk control I er with three 91 million-
byte disk drive units.
Additio.nal controller allowing dual
access of 7265/7266 disk drives, if
dual access feature 1035 is installed
(optional).
7265
1035
General Description
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