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TABLE 4-2. CARTRIDGE DISK
UNIT
SPECIFICATIONS/CHARACTERISTICS
SEEK TIME:
9msec. (minimum), 35msec. (average), 65msec. (maximum)
LATENCY TIME:
12.511 (average rotational latency)
TRANSFER RATE:
2,500,000 bits/sec. (adapter to disk drive), 312,500 bytes/sec., and 156,250
words/sec (MDC to memory)
DATA CAPACITY UNFORMATTED:
7500 bytes/track
DATA CAPACITY FORMATED:
256 bytes/sector
576 bytes/sector
(24 sectors/track)
(12 sectors/track)
Bytes/Track
6144 bytes
6192 bytes
Bytes/Disk Platter
100tpi
2,506,752 bytes
2,820,096 bytes
200tpi
5,013,504 bytes
5,640,192 bytes
SIMULTANEITY:
During data transfer on one unit, simultaneous seek operations can be
performed on all other units attached to the same controller
DISKS PER CARTRIDGE:
One (fixed and removeable)
RECORDING SURF ACES:
Per cartridge; two
CYLINDERS:
Per recording surface; 204 or 408
TRACKS:
Per cylinder; two or four
CARTRIDGE DISK USED:
M4024
PHYSICAL DIMENSIONS:
8.75 in. (24cm) high; 19 in. (48.2) wide; 30 in. (76,2cm) deep
Weight 85 pounds (38.6)
as to whether the transfer of data is input or
output. For all other commands, the direction bit
is ignored by hardware (see Figure 4-3).
CHANNEL NUMBER
r~-----------~----------~~
I
I
I
I
I
MSC PORT NUMBER ---,
I
~I
I I I
I I
\1
,-.-=--=-~-=-~--=--
__
,,_~-'-==~=~~-=--~)---'-----'-T""""'~
01 RECTI ON BIT
-L _ _
O-READ (INPUT)
SWITCH SELECTABLE
1-WRITE (OUTPUT)
MSC IDENTIFIER
Figure 4-3. Channel Assignments
A basic cartridge disk subsystem consists of a
mass storage controller, and a single adapter. Two
or more drives in the system are completely
software independent of one another in that a
system command will be accepted by a channel
that is not busy. This is because the MSC circuitry
is shared simultaneously by all four disks attached
to it (see Figure 4-3). The MSC91 0 I controller
will accept instructions from one drive while
another drive is in the process of transferring
data. However, the transfer of data on a drive
must be completed before any new data can be
accepted and processed by that drive. All other
operations are executed concurrently. If an MSC
is configured with less than four disks, it will
respond to channel numbers associated only with
the devices installed.
CARTRIDGE DISK UNITS
All data transfers are executed in the DMA
mode and are normally in word mode. However,
byte mode transfers can occur if associated with
the first and/or last memory cycle of a particular
data transfer provided that the main memory
buffer begins or ends on an odd byte boundary.
BASIC TRACK FORMAT
Each track on the drive contains 12 or 24
equal length sectors of 256 or 576 bytes respec
tively. There are 204 or 408 cylinders per surface
and two or four tracks per cylinder yielding a
total
formatted
capacity
of 2,506,752
to
11,280,384 bytes, respectively. The data en
coding scheme is double frequency recording and
each field is preceded by a SYNC word and
followed by an EDC (Error Detection Code) word
and postamble. The basic track format is shown
in Figure 4-4.
PERIPHERAL COMMANDS
Two configuration words are required for
control of the disk drives (see Figure 4-5).
Configuration words A and B contain the image
of the ID field of the sector on which a particular
operation is initiated. The cylinder number (bits
7-15) and p"Iatter select (bit four) in Configura
tion Word A are used as the seek argument for
seek operations. The sector number field of
Configuration Word B (bits 8-15) is incremented
AT04
4-3
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