Can't count on your fingers
October 12th, 2008
Question: What was unusual about the way the IBM 1620 (a transistorized computer introduced by IBM in 1960) did arithmetic?
- The 1620 stored all numbers as alphabetic characters.
- The 1620 had a 36-bit accumulator with 2 overflow bits.
- The 1620 had no Arithmetic Logic Unit (ALU).
- The 1620 represented negative numbers in ones-complement form.
Answer: The 1620 had no Arithmetic Logic Unit (ALU).
Arithmetic was done by table lookup one decimal digit at a time. Multiplication and addition tables had to be loaded into memory before the machine ran a program. The code name for the 1620 was CADET: Can't Add Doesn't Even Try.
Entry Filed under: Trivia