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IBM 701 Electronic Data Processing Machine

Overview

The IBM 701, originally developed under the codename “Defense Calculator”, was IBM’s first commercial scientific computer and its first series-production mainframe. It was announced to the public on May 21, 1952, and was the first in the IBM 700/7000 series, which remained IBM’s high-end line until the System/360 arrived in 1964.

Key People

  • Nathaniel Rochester – co-designer and co-developer
  • Jerrier Haddad – co-designer and co-developer
  • John von Neumann – recommended adding the magnetic drum unit to reduce I/O bottlenecks; the 701 was based on his IAS machine at Princeton
  • Thomas Watson Jr. – championed the project; noted at the 1953 IBM stockholders’ meeting that “as a result of our trip, on which we expected to get orders for five machines, we came home with orders for 18”

Technical Specifications

Parameter Value
Word size 36 bits (or 18-bit half-word)
Instruction length 18 bits, single-address format
Opcode 5 bits (32 instruction types)
Address 12 bits (4096 half-word addresses)
Number representation Signed magnitude, fixed-point
Precision ~10 decimal digits per full word
Registers 2: Accumulator (38 bits, 2 overflow bits) and Multiplier/Quotient (36 bits)
Primary memory 72 Williams tubes x 1024 bits each = 2048 words of 36 bits
Williams tube diameter 3 inches
Memory cycle time 12 microseconds
Max memory 4096 words (with second set of Williams tubes or magnetic-core upgrade)
Addition time 60 microseconds (5 cycles, 2 of which are refresh)
Multiply/divide time 456 microseconds (38 cycles)
Logic technology Vacuum tubes (1071 visible in processor frame)
Weight ~20516 pounds (10.3 short tons / 9.3 metric tons)
Power Not specified in available sources; multiple power units (IBM 736, 741, 746)

Williams Tube Memory

The Williams tube storage was electrostatic, storing bits as charge patterns on the phosphor face of cathode ray tubes. Each tube held 1024 bits. The tubes required periodic refreshing, which forced refresh cycles into the 701’s timing – two of the five cycles in an addition were refresh cycles.

Later, the IBM 737 Magnetic Core Storage unit could replace the Williams tubes, providing 4096 words at the same 12-microsecond cycle time.

System Configuration

Unit Function Notes
IBM 701 CPU / Analytical Control Unit  
IBM 706 Electrostatic Storage 2048 words, Williams tubes
IBM 711 Punched Card Reader 150 cards/min
IBM 716 Printer 150 lines/min
IBM 721 Punched Card Recorder 100 cards/min
IBM 726 Magnetic Tape Reader/Recorder 100 bits/inch
IBM 727 Magnetic Tape Reader/Recorder 200 bits/inch
IBM 731 Magnetic Drum Reader/Recorder Recommended by von Neumann
IBM 737 Magnetic Core Storage 4096 words, 12 us cycle
IBM 740 CRT Output Recorder  
IBM 753 Magnetic Tape Control Controls up to 10 IBM 727s
IBM 736, 741, 746 Power units  

Production and Cost

  • Units shipped: 19
  • Release date: 1952 (first deliveries 1953)
  • Rental: ~$12000/month (Aviation Week, May 1953); $15000/month for one 40-hour shift, $20000/month for two shifts (American Aviation, November 1953). Approximately $144000/month in 2025 dollars.

Customer List (all 19 installations)

  1. IBM World Headquarters, New York, NY
  2. University of California, Los Alamos, NM
  3. Lockheed Aircraft, Glendale, CA
  4. National Security Agency, Washington, DC
  5. Douglas Aircraft, Santa Monica, CA
  6. General Electric, Lockland, OH
  7. Convair, Fort Worth, TX
  8. U.S. Navy, Inyokern, CA
  9. United Aircraft, East Hartford, CT
  10. North American Aviation, Santa Monica, CA
  11. RAND Corporation, Santa Monica, CA
  12. Boeing Corporation, Seattle, WA
  13. Douglas Aircraft, El Segundo, CA
  14. Naval Aviation Supply, Philadelphia, PA
  15. University of California, Livermore, CA
  16. General Motors, Detroit, MI
  17. Lockheed Aircraft, Glendale, CA (second unit)
  18. U.S. Weather Bureau, Washington, DC
  19. DuPont Central Research, Wilmington, DE

The customer base was overwhelmingly defense and aerospace, consistent with the “Defense Calculator” origins.

Design and Construction History

The 701 was based on the IAS machine designed by von Neumann at the Princeton Institute for Advanced Study. IBM’s design team, led by Rochester and Haddad, adapted the architecture for commercial production. The first magnetic tape drives were adapted from IBM’s Tape Processing Machine (TPM).

The machine competed with Remington Rand’s UNIVAC 1103 in the scientific computation market. In early 1954, the Joint Chiefs of Staff commissioned comparative trials for the Joint Numerical Weather Prediction (JNWP) project. The trials showed comparable computational speed (with a slight IBM advantage), but the 701 was unanimously favored for its significantly faster I/O equipment.

Key Innovations

  • IBM’s first commercial stored-program electronic computer
  • First in the 700/7000 series line that dominated scientific computing for a decade
  • Williams tube electrostatic storage (later upgradeable to magnetic core)
  • Transition vehicle that moved IBM from punch-card tabulators to electronic computing

Science and Applications

Georgetown-IBM Machine Translation Experiment (1954)

In 1952, IBM partnered with Georgetown University linguists. On January 7, 1954, the team demonstrated experimental software that translated Russian to English on the 701. The Mark 1 Translating Device (for the U.S. Air Force) produced its first automated Russian-to-English translation in 1959 and was shown publicly in 1964.

Blackjack Optimal Strategy (1954)

A group of scientists ran millions of simulated blackjack hands on an IBM 701 to determine the best playing decision for every card combination. The resulting set of correct rules for hitting, standing, doubling, and splitting remains the foundation of basic blackjack strategy today.

Artificial Intelligence – Samuel’s Checkers (1956)

Arthur Samuel’s checkers-playing program was demonstrated on February 24, 1956, representing the first computer to display the potential of artificial intelligence. The program was later shown on television. (Samuel continued the work on later IBM machines; in 1962 the program defeated self-proclaimed checkers master Robert Nealey on an IBM 7094.)

Nuclear Research

At Lawrence Livermore National Laboratory, the IBM 701 enabled scientists to run nuclear explosives computations faster than ever before.

Weather Forecasting

The U.S. Weather Bureau’s installation (unit 18) was used in support of the nascent JNWPU operational forecasting program.

Programming Languages

  • Speedcode (1953) – first high-level programming language for an IBM computer, developed by John Backus to support floating-point operations
  • KOMPILER – compilation and runtime system developed by the UC Radiation Laboratory at Livermore
  • John Backus also began FORTRAN development on the 701, but it was not released until the IBM 704

Notable Anecdotes

  • Watson Jr.’s sales trip expecting 5 orders and returning with 18 became a legendary IBM story about underestimating demand for scientific computing.
  • The 701 weighed over 10 tons – roughly the weight of a loaded cement truck.
  • The “Defense Calculator” name reflected IBM’s awareness that Cold War defense spending would drive demand; the neutral “701” designation was adopted for public release.

Current Status

A Williams tube from an IBM 701 is preserved at the Computer History Museum in Mountain View, California. No complete surviving 701 systems are known.

Sources