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Table 2 Characteristi cs (cont.)
Operati ng Characteri sti cs (cont.)
Nominal access time
(positioning)
Seek
Rotational latency
T ronsfer rates
Instantaneous (per
sector)
Average (multiple sector)
12 msec track to ad-
jacent track
38 msec average
(12-75 msec)
12.5 msec (0-25 msec)
312,000 bytes/second
230,000 bytes/second
Physical Characteristics
Standard equipment cabinet
Height
Width
Depth
Mode I 7250 Contra lIer
Height
Width
Depth
Weight
Model 7251/7252 DiskDrive
Height
Width
Depth
Weight
63.5 in.
4
,Jp
~
32 in.
!
p+ ---...
35 in.
V'O
~
20 in.
24 in.
10 in.
40
Ib
10.3 in.
17.5 in.
28.5 in.
150lb
Environmental Characteristics
Power requirements
Service
Start
Run
Operati ng temperature
Operating humidity (relative)
Therma I di ssi pati on
Model 7250
Model 7251;7252
Cable lengths (lOP to 7250)
120 vac, 60 Hz,
single-phase
1.8 kva
Controller, 250 watts
Drive, 800 watts
5cP
to 104
0
F
(1
(1)
to
4cP
C)
25% to 8()oA,
850 btu,Au
160 btu,/hr
40
ft maximum
Table 2. Characteristics (cont.)
Operating and Physical Characteristics
of Model 7254 Disk Cartridge
Recording surfaces/cartridge
2
Disk surface coating
Magnetic: oxide
Di sk cartri dge
Diameter
15.01 in.
~g2
---
Height
2.4 in.
'i~·
Weight
5 Ib
,11
27
/1
The
mini mum configuration
(2.3
mi lIionl
bytes)
i,
One 7250 controller
One 7251 disk drive
One 7254 di sk cartri dge
!
i
The maximum configuration (18.4 mi Ilion bytes) is
One 7250 controller
Four 7252 di sk drives
Four 7254 disk cartridges
Auxi liary equipment includes a multiple-drive selection
unit, a power distribution panel, a power filter, a PT20C
power supply, and the required cables.
The controller permits the intermixing of 7251 and 7252 disk
drives.
Disk drives are the electro-mechanical devices
containing the read, write, and control circuitry required
to record data on disk surfaces. The controller and two
drives share a standard Xerox cabinet; additional drives
are housed in additional cabinets.
The 7251 disk drive provides a total storage capacity of
2.3 million bytes and is the drive mechanism for the disk
cartridge. The drive is mounted in a drawer that slides out
in order to load and unload cartridges and to service the
equipment.
The 7252 drive differs from the 7251 by
providing on additional 2.3 mi Ilion bytes of fixed disk
storage - a second disk shares the head positioner and
the spindle with the cartridge.
The 7254 contains a single disk enclosed in protective
covers.
After removing the bottom cartridge cover and
pulling out the equipment drawer, the cartridge may be
loaded onto the drive spindle from the top.
Introduction
3
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