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1. GENERAL DESCRIPTION
INTRODUCTION
XDS Model 7240/7242/7246 Removable Disk Storage Sys-
tem provides high-volume, random-occess storage.
It is a
moving-arm, removable-medium, rotating magnetic disk
system used as secondary storage for Sigma computers.
Model 7240Controller controls up to four Model 7242/7246
storage units and permits execution of the orders reguired
to use this system. Optional Model 7243/7247 Device
Pooling Feature permits two computers or one computer
with two Model 7240 controllers to have simultaneous
access to any two spindles out of a maximum of eight inde-
pendent spindles.
Optional Model 7241 Extended Width
Interface allows the system to operate in a 4-byte p.:irallel
format in conjunction with the appropriate Input/Output
Processor (!OP).
To use this manual effectively, the reader should be famil-
iar with the Sigma Computer Reference Manual applicable
to his installation, particularly the discussion of input/
output instructions and operal"ions.
SYSTEM COMPONENTS
A system consists of some combination of the following
components:
Model No.
7240
7241
7242
7243
7244
7246
7247
Component
Disk Storage Controller
Extended Width Interface (optional)
Disk Storage Unit (dual spindle)
Device Pooling Feature (dual spindle)
(optional)
Removable Disk Pack
Disk Storage Unit (single spindle)
Device Pooling Feature (single spindle)
(optional)
Model 7240 Controller serves one to eight spindles com-
posed of Model 7242 and 7246 storage units (maximum of
four units) and is attached to one channel on an !OP.
Model 7241 permits data transfers with an !OP on a 32-bit
basis.
Model 7243/7247 Device Pooling Feature may be
added to Model 7242/7246 to provide dual access by two
controllers. This allows simultaneous read/read, write/
write, or read/write on any two spindles.
Model 7244
Disk Pack is the removable storage medium, consisting of
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11 disks with 20 usable recording surfaces. The disk pack
has a special indexing ring to provide reference points for
the 6-sector recording format.
A minimum configuration consists of one Model 7240 Con-
trol
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er and one Model
72~2
or 7246 storage unit.
• Table 1. Characteristics
Operating Characteristics
Recording format
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1024 bytes/sector
6 sectors/track
203 tracks/surface
1 head/surface
20 recording surfaces/pack
Recording method
Track serial
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Mode
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Double frequency NRZ
Recording Frequency
2.50 Mhz
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Rotational speed
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2400 rpm
Model 7246 (single
!
spindle)
24 ,576,000 bytes
Model 7242 (dual
spindle)
49, 152,000 bytes
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Maximum system
(4 units, i.e.,
8 spi nd
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es/control
le~)
l 96,608,000 bytes
Access(positioning) time
Maximum
135 ms
Maximum access time
between adjacemt
tracks
24.5 ms
Average
75 ms
Transfer rate
Single sector
312,500 bytes/second
Multiple sectors
(average)
250 ,800 bytes/second
Physica I Charac teri sti cs
Model 7240 (space pro-
vided for 7241)
Height
63.5 in.
Width
32 in.
Depth
35 in.
Weight (approx.)
500 lb
General Description
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