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manual, particularly the, . . chapters on input/output instruc-
tions and operations; see "Related Publications" at the
front of this manual.
fEATURES
Several significant equipment features affect system per-
formance and the reliability of recorded data:
•
A fully integrated spindle;blower assembly contributes
to excellent device reliability.
•
A noncontacting transducer ensures accurate and re-
liable control of the head positioner.
•
The transfer rate of 312,000 bytes/second is normally
available only on more expensive disk systems.
•
An integrated controller maintenance panel faci litates
off-I i ne servi ci
ng
of the equi pment •
•
Stray magnetic flux at the read/write heads is negli-
gible, eliminating a common cause of disk errors.
•
The disk contents are permanently protected against
primary power failure.
Other features that have programming implications:
•
Each disk contains 408 tracks and each track is
divided into 16 sectors.
•
Data are recorded on the disk surfaces in fixed-length
sectors of 360 bytes. The controller zero-fills the
sector for a record of less than 360 bytes.
•
The controller automati cally increments sector and
track addresses, and hence a record can extend from
sector to sector and from track to track.
•
Access time is 12 msec, track to adjacent track, and
38 msec average.
I.
A write-protect feature ensures total fi Ie protection.
•
The simplified system design makes I/O programming
less complex than that required for conventional disk
systems.
SYSTEM COMPONENTS
Table 1 summarizes the system components described in this
section, while Table 2 presents the operating, physical,
and environmental characteristics.
2
Introducti on
I
Table 1. Cartridge Disk System Components
Prerequisite
Model
Component
Component
7250
Controller that serves up to
lOP channel
four Model
7251j7252
Di sk
Drives
7251
Disk Drive providing a stor-
7250
age capacity of 2.3 mi Ilion
bytes.
Employs the Model
7254 Disk Cartridge.
7252
Disk Drive providing a stor-
7250
age capacity of 4.6 million
bytes.
Employs the
Mode I 7254 Disk Cartridge,
as well as a fixed disk.
7254
Disk Cartridge containing a
7250, and
single disk (one plate with
ei ther a 7251
two recording surfaces).
or a 7252
I
Tab Ie 2. Characteristics
Operating Characteristics
Recording format
360 bytes/sector
16 sectors/track
2 tracks/cylinder
204 tracks/surface
1 head/surface
2 recordi ng surfaces/
disk
Density
lateral track
100 trocks/.nch
Capacity (Innermost track)
2200 bits/.nch
Recording method
Track serial
Mode
Double frequency
Recording frequency
2.50 Mhz
Rotational speed
2400 rpm
I
Total time per revolution
25 msec
Intersectorgap time
203
~ec
Sector-to-sector time
1.56 msec
Effective read/wri te bit rate
2,500,000 bits/second
On-line capacity (sectored)
2,350,000 bytes/disk
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