Software Development at the Eckert-Mauchly Computer Company Between 1947 and 1955

Iterations – Norberg – Software Development at EMCC 

 7 

megacycles.

17

 Word sizes varied from 52 pulses per word to 104, with C-

10 ending at 91 pulses per word. C-1 called for 50 20-word mercury delay 

tanks, which in C-10 became 100 10-word tanks. Block size climbed from 

20 words initially to 60 at the end. As Snyder noted, the characteristics 

that remained fixed throughout the code definitions were: 

 

The handling of decimal quantities 

Using excess 3 addition 

The handling of coded alphabetic 

Memory size from 1,000 to 100,000 words (4 digits) 

Tape servos for input and output 

Parallel read-write and compute 

Buffer between input, output, and memory 

12-character digit words 

2 instructions per word 

directly connected typewriter.

18

  

 

To illustrate the differences in characteristics among the three major 

EMCC designs of the 1940s, Figure 1 shows a comparison of the features 

of the various Eckert-Mauchly designs compiled by Nancy Stern for her 

study of EMCC and the sources for the data.

19

  

 

Programming the IBM Defense Calculator 

 

It is instructive at this point to compare these activities inside EMCC with 

those occurring inside IBM while they designed programming for the new 

Defense Calculator, the system delivered at the end of 1952. Developed in 

1951-52, the Defense Calculator, later called the IBM 701, was similar to 

the Princeton IAS design, but deviated from it in a number of ways. 

Designs for tape systems to be used with other systems suggested a 36-bit 

word length would allow the computer to use these tape systems, rather 

than requiring design of new storage. This word length allowed two 18-bit 

instructions per word. Addresses in this design could be assigned to each 

18-bit half-word, and branch instructions fell naturally into the addressing 

scheme. Various techniques were devised to maximize the use of 

input/output systems without delaying internal operations of the system. 

Punch cards contained both data and instructions and these were read into 

the system while the CPU continued to operate on instructions.

20

  

 

With IBM’s Engineering-Applied Science group, a mathematical 

programming study proceeded to review the Defense Calculator design to 

develop programs to enhance the utility of the system to customers. The 

group either developed or adopted programs from other IBM systems for 

use with the Defense Calculator. Among these were programs for floating-

point, complex and double precision arithmetic, and the extraction of 

roots. They designed complete application programs, a solution of 

Laplace’s equation, and a partial differential equation program applicable 

to determining the distribution temperature in a nuclear reactor. Many new 

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Iterations – Norberg – Software Development at EMCC 

 8 

A COMPARISON OF ARCHITECTURE, PERFORMANCE, AND PHYSICAL 

CHARACTERISTICS OF THE ECKERT-MAUCHLY COMPUTERS

 

 

 

EDVAC BINAC  UNIVAC 

ARCHITECTURE 

 

 

 

Programming 

Stored program 

Stored program 

Stored program 

Data Transmission 

Serial 

Serial 

Serial 

Number representation 

Binary 

Binary 

Decimal 

Word Length 

44 bits 

31 bits 

11 digits + sign 

Other data types 

- 

- 

12 characters/words 

Instruction length 

44 bits 

14 bits 

6 characters 

Instruction format 

4-address 

1-address 

1-address 

Instruction set size* 

12(16) 

25(32) 

45(63) 

Accumulators/programmable registers  4 

2 

4 

Main memory size 

1,024 words 

512 words 

1,000 words 

Main memory type 

Delay line 

Delay line 

Delay line 

Secondary memory 

Magnetic drum 

Magnetic tape 

Magnetic tape 

Other I/O devices 

Cards, paper tape  Typewriter 

Typewriter, cards, paper tape 

Error detection 

Redundant CPUs  Redundant CPUs  Redundancy, parity 

 

 

 

 

PERFORMANCE 

 

 

 

Clock rate 

1 MHz 

4 MHz‡ 

2.25 MHz 

Add time 

0.864 ms† 

0.285 ms† 

0.525 ms† 

Multiply time 

2.9 ms† 

0.654 ms† 

2.15 ms† 

Divide Time 

2.9 ms† 

0.633 ms† 

3.89 ms† 

 

 

 

 

PHYSICAL CHARACTERISTICS  

(approximate measurements) 

 

Vacuum tube count 

3,600 

1,400 

5,400 

Diode count 

12,000 

N/A 

18,000 

Power consumption 

50 kW 

13 kW 

81 kW 

Floor space of computer only 

490 sq. ft. 

N/A 

352 sq. ft. 

 

Figure 1. Adapted from Nancy Stern, From Eniac to UNIVAC: An Appraisal of the Eckert-

Mauchly Computers (Bedford, Mass.: Digital Press, 1981). 

 

KEY: 

 

N/A—data not available. 

*—number of instructions used (number encoded). 

†—includes memory access time for instructions and operands. 

‡—later reduced to 2.5 M

 

 

instructions were proposed, not necessarily to provide for new problem 

solution techniques, but rather to offer programs that would make 

previously attempted problems easier to solve.

21

  

 

Two significant comparisons should be made here. First, a number of the 

programs developed were similar or identical to those proposed by EMCC 

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