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SECTION I.
INTRODUCTION
CENTRAL PROCESSOR
The central processor is the computing and control center of the Model 120; instructions
-......;
processed within the central processor control the operations of the entire system!
The Model
120 processor is functionally divided into three units:
storage, control, and arithmetic.
The
storage unit provides magnetic core storage for both the program instructions and the data to
be processed according to these instructions; it is also used to contain the resultant data.
The
control unit directs the operation of the entire computer by selecting, interpreting, and con-
trolling the execution of all program instructions.
It controls not only the flow of information
within the central processor, but also the flow of data between the central processor and all
peripheral equipment.
The arithmetic unit performs such operations as addition, subtraction,
multiplication, division, and comparison, as directed by the control unit.
Included as part of the central processor is a control panel (see Section II) which provides
for easy communication between the operator and the computer.
By using various control
switches, the operator can start and stop the machine and can load and interrogate locations in
memory.
The addition of an operator's console to a Model 120 makes further monitoring and control
facilities available to the operator and increases the scope and power of the associated central
processor.
The Type 220-1 and 220-3 Consoles perform the same basic functions as a control
panel and provide the capability for some important auxiliary operations as well (see Section VIII).
PERIPHERAL DEVICES
The basic Model 120 can be equipped with a card reader, a card punch, and a printer -
connected to the central processor by means of integrated peripheral controls.
Information is
transferred between anyone of these devices and the central processor by means of Peripheral
Data Transfer (PDT) instructions.
By coding various control characters in this instruction,
the programmer specifies the direction of data transfer (into or out of the processor), the
specific device involved in the transfer, the data path over which information is to be transferred,
and any other information necessary to define the input/ output operation (e. g., the number of
lines to be spaced during printer operations).
The actual communication with the central pro-
cessor is not made by the particular device but by the peripheral control associated with that
device.
A peripheral control regulates the transfer of data between a processor and a peripheral
device.
The control compensates for the difference in the data transfer rates of the processor
and the peripheral device by temporarily storing each character of transmitted information
until either the processor or the device is ready to receive the character.
The control also
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