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The
IBM
1620 Data Processing System is an electronic
computer system designed for scientific and techno-
logical applications. The use of solid-state circuit
components and the availability of from 20,000 to
60,000 positions of core storage provide the 1620
System with the capacity, reliability, and speed to
solve problems that in the past have required the use
of larger and more expensive data processing systems.
Actually, there are two 1620 Data Processing Systems,
the 1620 Modell and the 1620 Model 2. This manual,
as its title infers, is concerned with the 1620-1. Infor-
mation on the 1620-2 is available in the
IBM
publica-
tion, A26-5781. Briefly, however, the 1620-2 consists
of the 1620-2 Central Processing Unit (cpu) and the
1625 Core Storage Unit. The 1620-2, which uses the
same input/output units as the 1620-1, possesses up
to four times the computing and processing speeds of
the 1620-1. The operating features of both systems
are almost identical and with the exception of the
1620-2 special features, Index Registers and Binary
Capabilities, complete programming compatibility
exists between the two. Thus, a user whose initial
requirements are within the range of the 1620-1 can,
with a minimum of effort, transfer his expanding work
load to the 1620-2.
The units of the 1620 System-and henceforth, we
are concerned only with Model I-are as follows:
The 1620
CPU
is the controlling unit of the system;
it contains arithmetic and logic circuitry, twenty-
thousand positions of core storage, an operator's con-
sole, and a console input/output typewriter.
The 1621 Paper Tape Unit reads and punches
8-track paper tape.
The 1622 Card Read-Punch reads and punches
80-column cards.
The 1443 Printer provides up to 120 or 144 char-
acters per line of printed output.
The 1627 Plotter provides a graphic output of
. digital data.
The 1623 Core Storage Unit provides 20,000 or
40,000 additional core storage positions for the
CPU.
All core storage data is available at random-no
sequential searching for the desired data is required
- and within microseconds (a microsecond,
f.Lsec,
is
one millionth of a second).
IBM 1620 Data Processing System
The 1311 Disk Storage Drive provides unlimited
random access storage for the cpu. Information stored
on removable disk packs is available within milli-
seconds ( a millisecond (ms) is one thousandth of a
second). Each disk pack has a storage capacity of
2,000,000 characters. The disk packs are easily inter-
changed by the operator.
Data and instructions entered into the system are
placed in core storage as decimal digits. Each position
of core storage can be addressed individually and
can store one digit of information by the use of a 6-bit
Binary-Coded-Decimal (BCD) code. The addressing
system provides for the selection of any digit, or
group of digits, in core storage. As a standard feature,
the 1620 computer processes alphabetic and special
characters.
The arithmetic and logic section of the computer is
direct~d
by the stored program. The computer uses
a 2-address instruction format. Each 12-digit instruc-
tion includes a 2-digit operation code and two 5-digit
addresses. Use of the 2-address format and automatic
sequential execution of the programmed instructions
simplifies programming and reduces the number of
instructions required to solve a problem. The se-
quence of operations may be altered at any point in
the program by unconditional or conditional branch
instructions. Conditional branch instructions provide
logical decisions through tests performed on a system
of indicators and switches set by the computer or by
the operator.
Addition, subtraction, and multiplication operations
are accomplished by a table look-up method, in which
Add and Multiply tables located in specified areas of
core storage are referred to automatically when arith-
metic operations are being performed. Division is
accomplished by a division subroutine or by the
Automatic Divide special feature.
The
IBM
1620 is a variable field length computer.
The
shorte~t
admissible field is two digits (a field is
a unit of information composed of related consecu-
tively addressed digits); the longest field can be
any number of digits within the capacity of available
core storage positions. Not only can data fields
be stored in core storage in varying sizes, but these
same variable fields can also serve as factors in all
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