The Mark I had 60 sets of 24 switches for manual data entry and could store 72 numbers, each 23 decimal digits long.[13] It could do three additions or subtractions in a second. A multiplication took six seconds, a division took 15.3 seconds, and a logarithm or a trigonometric function took over one minute.
The Mark I read its instructions from a 24-channel punched paper tape and executed the current instruction and then read in the next one. It had no conditional branch instruction. This meant that complex programs had to be physically long. A loop was accomplished by joining the end of the paper tape containing the program back to the beginning of the tape (literally creating a loop). This separation of data and instructions is known as the Harvard architecture (although the exact nature of this separation that makes a machine Harvard, rather than Von Neumann, has been obscured with the passage of time, see Modified Harvard architecture). The first programmers of the Mark I were computing pioneers Richard Milton Bloch, Robert Campbell, and Grace Hopper.[14]
Instruction format[edit]
The 24 channels of the input tape were divided into three fields of eight channels. Each accumulator, each set of switches, and the registers associated with the input, output, and arithmetic units were assigned a unique identifying index number. These numbers were represented in binary on the control tape. The first field was the binary index of the result of the operation and the second, the source datum for the operation. The third field was a code for the operation to be performed.[13]
Aiken and IBM[edit]
Aiken published a press release announcing the Mark I listing himself as the sole "inventor". James W. Bryce was the only IBM person mentioned, even though several IBM engineers including Clair Lake and Frank Hamilton had helped to build various elements. Thomas J. Watson was enraged, and only reluctantly attended the dedication ceremony on August 7, 1944.[15][16] Aiken, in turn, decided to build further machines without IBM's help, and the ASCC came to be generally known as the Harvard Mark I. IBM went on to build the Selective Sequence Electronic Calculator (SSEC) to both test new technology and provide more publicity for the company.[15]
Successors[edit]
The Mark I was followed by the Harvard Mark II (1947 or 1948), Mark III/ADEC (September 1949), and Harvard Mark IV (1952) – all the work of Aiken. The Mark II was an improvement over the Mark I, although it still was based on electromechanical relays. The Mark III used mostly electronic components—vacuum tubes and crystal diodes—but also included mechanical components: rotating magnetic drums for storage, plus relays for transferring data between drums. The Mark IV was all-electronic, replacing the mechanical components with magnetic core memory. The Mark II and Mark III went to the US Navy base at Dahlgren, Virginia. The Mark IV was built for the US Air Force, but it stayed at Harvard.
The Mark I was eventually disassembled, although portions of it remain at Harvard in the Science Center. It is part of the Harvard Collection of Historical Scientific Instruments
The Mark I had 60 sets of 24 switches for manual data entry and could store 72 numbers, each 23 decimal digits long.[13] It could do three additions or subtractions in a second. A multiplication took six seconds, a division took 15.3 seconds, and a logarithm or a trigonometric function took over one minute.
The Mark I read its instructions from a 24-channel punched paper tape and executed the current instruction and then read in the next one. It had no conditional branch instruction. This meant that complex programs had to be physically long. A loop was accomplished by joining the end of the paper tape containing the program back to the beginning of the tape (literally creating a loop). This separation of data and instructions is known as the Harvard architecture (although the exact nature of this separation that makes a machine Harvard, rather than Von Neumann, has been obscured with the passage of time, see Modified Harvard architecture). The first programmers of the Mark I were computing pioneers Richard Milton Bloch, Robert Campbell, and Grace Hopper.[14]
Instruction format[edit]
The 24 channels of the input tape were divided into three fields of eight channels. Each accumulator, each set of switches, and the registers associated with the input, output, and arithmetic units were assigned a unique identifying index number. These numbers were represented in binary on the control tape. The first field was the binary index of the result of the operation and the second, the source datum for the operation. The third field was a code for the operation to be performed.[13]
Aiken and IBM[edit]
Aiken published a press release announcing the Mark I listing himself as the sole "inventor". James W. Bryce was the only IBM person mentioned, even though several IBM engineers including Clair Lake and Frank Hamilton had helped to build various elements. Thomas J. Watson was enraged, and only reluctantly attended the dedication ceremony on August 7, 1944.[15][16] Aiken, in turn, decided to build further machines without IBM's help, and the ASCC came to be generally known as the Harvard Mark I. IBM went on to build the Selective Sequence Electronic Calculator (SSEC) to both test new technology and provide more publicity for the company.[15]
Successors[edit]
The Mark I was followed by the Harvard Mark II (1947 or 1948), Mark III/ADEC (September 1949), and Harvard Mark IV (1952) – all the work of Aiken. The Mark II was an improvement over the Mark I, although it still was based on electromechanical relays. The Mark III used mostly electronic components—vacuum tubes and crystal diodes—but also included mechanical components: rotating magnetic drums for storage, plus relays for transferring data between drums. The Mark IV was all-electronic, replacing the mechanical components with magnetic core memory. The Mark II and Mark III went to the US Navy base at Dahlgren, Virginia. The Mark IV was built for the US Air Force, but it stayed at Harvard.
The Mark I was eventually disassembled, although portions of it remain at Harvard in the Science Center. It is part of the Harvard Collection of Historical Scientific Instruments
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