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Chapter 13

UNIVAC Scientific (1103A) instruction logic'

John W Carr III

The UNIVAC Scientific computer is a (35, 0, 0)2 binary machine, with option of (27, 8, 0). The arithmetic unit contains two 36-bit X (exchange) and 9 (quotient) registers and one 72-bit A register (accumulator). Negative numbers are represented in one's complement notation.

Input-output is via high-speed paper tape reader and punch, direct card reader and punch, and Uniservo magnetic tape units, which may be connected to peripheral punched card readers and punches and a high-speed printer. In addition, information may be recorded on magnetic tape directly from keyboards by the use of Unitypers. Communication with external equipment is via an 8-bit (IOA) register and a 36-bit (IOB) register. Information sent to these registers controls magnetic tapes as well as other input output equipment. The program address counter (PAK) contains the present instruction address. Storage is in up to 12,288 locations of magnetic core storage, along with a directly addressable drum of 16,384 locations. Instructions are of the two-address form, with six bits for the operation code and two fifteen-bit addresses (u and v).

The following information is taken from a Univac Scientific Manual [Univac Scientific Electronic Computing System Model 1103A, Form EL338].

Definitions and conventions

Instruction word

oc Operation code
u First execution address
v Second execution address

For some of the instructions, the form jn or jk replaces the u ad dress; for others the form k replaces the v address.

j One-digit octal number modifying the instruction
n Four-digit octal number designating number of times instruction is to be performed
k Seven-digit binary number designating the number of places the word is to be shifted to the left

Fixed addresses

F1 00000 or 40001
F2 00001
F3 00002
F4 00003

Arithmetic section registers

A 72-bit accumulator with shifting properties
AR Right-hand 36 bits of A
AL Left-hand 36 bits of A
Q 36-bit register with shifting properties
X 36-bit exchange register

Note: Parentheses denote contents of. For example, (A) means contents of A (72-bit word in A); (Q) means contents of 9 (36-bit word in Q).

1In E. M. Grabbe, S. Ramo, and D. E. Wooldridge (eds.), "Handbook of Automation, Computation, and Control," vol. 2, chap. 2, pp. 77-83, John Wiley & Sons, Inc., New York, 1959.
2Carr's triplet notation for: fractional significant digits, digits in exponent, and digits to left of radix point.


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