IBM 701 - Description

Description

The system used electrostatic storage, consisting of 72 Williams tubes with a capacity of 1024 bits each, giving a total memory of 2048 words of 36 bits each. Each of the 72 Williams tubes was three inches in diameter. Memory could be expanded to a maximum of 4096 words of 36 bits by the addition of a second set of 72 Williams tubes or by replacing the entire memory with magnetic core memory. The Williams tube memory and later core memory each had a memory cycle time of 12 microseconds. The Williams tube memory required periodic refreshing, mandating the insertion of refresh cycles into the 701's timing. An addition operation required five 12 microsecond cycles, two of which were refresh cycles, while a multiplication or division operation required 38 cycles (456 microseconds).

Instructions were 18 bits long, single address.

• Sign (1 bit) - Whole word (-) or Half word (+) operand address
• Opcode (5 bits) - 32 instructions
• Address (12 bits) - 4096 Half word addresses

Numbers were either 36 bits or 18 bits long, signed magnitude, fixed point.

The IBM 701 had only 2 programmer accessible registers:

1. The accumulator was 38 bits long (adding 2 overflow bits).
2. The multiplier/quotient was 36 bits long.

The IBM 701 system was composed of the following units:

• IBM 701 - Analytical Control Unit (CPU)
• IBM 706 - Electrostatic Storage Unit (2048 words of CRT Memory)
• 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
• IBM 736 - Power Frame #1
• IBM 737 - Magnetic Core Storage Unit (4096 words of Core Memory)
• IBM 740 - Cathode Ray Tube Output Recorder
• IBM 741 - Power Frame #2
• IBM 746 - Power Distribution Unit
• IBM 753 - Magnetic Tape Control Unit (controlled up to ten IBM 727s)

Nineteen IBM 701 systems were installed. The University of California at Livermore developed a language compilation and runtime system called the KOMPILER for their 701. A Fortran compiler was not released by IBM until the IBM 704.

The 701 can claim to be the first computer displaying the potential of artificial intelligence in Arthur Samuel's Checkers-playing Program.

IBM 701 competed with Remington Rand's ERA 1103 in the scientific computation market, which had been developed for the NSA, so held secret until permission to market it was obtained in 1953. In early 1954, a committee of the Joint Chiefs of Staff requested that the two machines be compared for the purpose of using them for a Joint Numerical Weather Prediction project. Based on the trials, the two machines had comparable computational speed, with a slight advantage for IBM's machine, but the latter was favored unanimously for its significantly faster input-output equipment.

The successor of the 701 was the index register-equipped IBM 704, introduced 4 years after the 701. The 704 was not compatible with the 701, however, as the 704 increased the size of instructions from 18 bits to 36 bits to support the extra features. The 704 also marked the transition to magnetic core memory.