Operations - IBM 7074 General Information Manual

Operations
The four basic commands used to perform all disk
storage and file control operations are: control, sense,
write and read.
Control
The 7631 File Control will decode and execute any of
13 orders transmitted from the computer by the con-
trol command. The 7631 decodes the transmitted order,
accepts address information, performs the designated
function, and then transmits an
END
or
UNUSUAL END
signal to the computer. In the case of a seek order, the
file control sends the
END
signal after decoding the
order. It then performs the seek, and at the comple-
tion of the seek operation, sends an
ATTENTION
signal
to the computer.
The orders consists of two or ten characters. For
operatIons where addresses are not required, only a
two-digit operation code is sent to the file control.
Orders requiring the two digit operation code only are:
no operation, release, six-bit mode, and eight-bit mode.
The orders, with their mnemonic code and their
numeric operation code are shown in Figure 8.
No Operation (DNOP-OO)
This order requires only the two-digit operation code.
The order is accepted by the 7631 as a programming
convenience only. No function is performed by the
7631 for this order.
Order
No Operation
Release
Eight-Bit Mode
Six-Bit Mode
Seek
Prepare to Verify, Single Record
Prepare to Write, Format
Prepare to Verify, Track with No Addresses
Prepare to Verify, Cyl inder Operation
(Optional Feature)
Prepare to Write Check
Set Access Inoperative
Prepare to Verify, Track with Addresses
Prepare to Verify, Home Address
Figure
8.
Table of Orders
10
Mnemonic Numeric
Code Code
DNOP 00
DREL
04
DEBM
08
DSBM
09
DSEK
80
DVSR
82
DWRF 83
DVTN
84
DVCY
85
DWRC
86
DSAI
87
DVTA
88
DVHA
89
Release (DREL-04)
This order requires only the two-digit operation code.
The order has meaning only for shared system opera-
tion. Whenever either system selects and gains control
of the 7631, it remains in control of that system until
the release order is issued, permitting the file control
to be available for either system.
Eight-Bit Mode (DEBM-08)
This order requires only the two-digit operation code.
The order conditions the file control to operate in the
eight-bit mode. This mode of operation is required
when the using system is operating in the packed
format mode. Packed format is the packing of two
numeric digits into one eight-bit character. The normal
data rate of the file control in the eight-bit mode is
70, 100 characters per second with a maximum of 2,165
data characters for data track capacity; when using
packed format, however, data rate is 140, 200 digits per
second with a maximum of 4,330 digits for a data track
capacity.
Six-Bit Mode (DSBM-09)
This order requires the two-digit operation code only.
The order conditions the file control to operate in the
six-bit mode. The data rate for the file control when
operating in the six-bit mode is 90,100 characters per
second with a maximum track capacity of 2,800 char-
acters.
Seek (DSEK-80)
The order for this operation causes the specified access
mechanism of the addressed module to locate itself at
the proper cylinder and to select the desired head.
When the order has been received by the file control,
it signals
END
and allows the computer to continue with
its own routine while disk storage executes the seek,
operation. A seek may be directed to other access
mechanisms on the disk storage units attached to the
same file control. An
UNUSUAL END
signal results if a
seek is given to an access mechanism in motion or if
the access mechanism is inoperative.
Upon completion of a seek operation, an
ATTENTION
signal is sent to the computer. In addition, a bit asso-
ciated with the access mechanism is set in status data
to indicate this condition. This indication is sent as part
of the status data transmitted in response to a sense
command. The attention indicator is reset when the
access is serviced by either a prepare to verify order
or another seek order.
The seek order, preceding a cylinder or full track
order, is not necessary when the current setting of the