Functions - IBM 7074 General Information Manual

Functions
The function performed by the 7631 File Control,
1301 Disk Storage, and the using system's data channel
are based on the execution of instructions, commands,
and orders, defined as follows:
Instruction: An instruction is system-coded informa-
tion that is decoded and executed by the central proc-
essing unit to perform a specific function.
Command: A command is system-coded information
that is decoded and executed by the data channel to
perform a specific function. (The 7080 system does not
use the term commands.)
Order: An order is control-coded information that is
decoded and executed by a control unit (file control,
in this case) to perform a specific function.
In the following description the word "command"
means "instruction" when applied to the 7080 system.
The file control can execute anyone of four com-
mands (read, write, sense, and control) . The ap-
plicable data processing system defines the method by
which the four commands are issued to the file control.
Read and write commands set up necessary control
circuits in the connecting data channel to permit trans-
mission of data between disk storage and the com-
puter system through the file control. The sense com-
mand causes transmission of status data from the file
control to the computer to indicate status of disk stor-
age and file control. The control command is used to
transmit orders to the file control.
Orders
Orders are transmitted to the file control by a control
command of the computer in the same manner as data
are normally transmitted. The file control recognizes
the information as an order, decodes it, and executes it.
Transmission of orders to the file control as a result
of the command is the same for all computer systems
using this file control, although the method by which
they are initiated may be different.
Orders normally consist of a two digit operation
code and eight characters to define addresses. When
address information is not required, the order consists
of the operation code only. Figure 7 shows the make-up
of the order.
Orders are transmitted from the computer's data
channel as
BCD
characters. The 7631 File Control
accepts the digit portion of the first eight characters of
the order (operation code, access and module number,
Operation Code
Access and Module Number
G'
"'~d
Add,""
'Xx' 'XX
xxxxxx'
Figure 7. Order
and the first four positions of the address) and all bits
in the ninth and tenth characters of the order.
Operation Code: A two-digit code that specifies the
operation to be performed. This portion of the order
is always numeric. The operation code is all that is
required for the following orders: no operation, six-bit
mode, eight-bit mode, and release.
Access and Module Number: These two positions of
the order, always numeric, specify the module in which
the operation will take place.
Record or Home Address: This portion of the order
gives the home or record address, depending upon the
type of operation that is to take place.
Operation Signals
Since disk storage operation takes advantage of the
interrupt feature of the 7000 series systems, signals are
generated to provide a communication link between
the file control and the computer. The signals, gen-
erated to indicate a specific condition exists, are:
Attention: Indicates that a previously given seek
operation has successfully positioned the access mech-
anism at the specified location and selected the desired
head.
End: Indicates the successful completion of an
operation. This signal can indicate the successful trans-
mission of an order to the file control, or it can indi-
cate the successful completion of a read or write
operation.
Unusual End: Always indicates an unsuccessful
operation. This signal can indicate that an error has
been sensed during a read or write operation, or any
other check condition has occurred, or it might indi-
cate that an unsuccessful attempt to transmit data has
occurred.
Stop: Indicates that the computer has sensed the end
of a read or. write field. The stop signal results from
the record definition word in a 7070 or 7074 system;
from the sensing of a group mark in a 7080 system;
and from word count equal zero in a 7090 system.
Introduction 9