1943 - January
The Harvard Mark I (originally ASCC Mark I, Harvard-IBM Automatic
Sequence Controlled Calculator) was built at Harvard University by Howard
H. Aiken (1900-1973) and his team, partly financed by IBM - it became the
first program controlled calculator. The whole machine is 51 feet long,
weighs 5 tons, and incorporates 750,000 parts. It used 3304
electromechanical relays as on-off switches, had 72 accumulators (each
with its own arithmetic unit) as well as mechanical register with a
capacity of 23 digits plus sign. The arithmetic is fixed-point, with a
plugboard setting determining the number of decimal places. I/O
facilities include card readers, a card punch, paper tape readers, and
typewriters. There are 60 sets of rotary switches, each of which can be
used as a constant register - sort of mechanical read-only memory. The
program is read from one paper tape; data can be read from the other
tapes, or the card readers, or from the constant registers. Conditional
jumps are not available. However, in later years the machine is modified
to support multiple paper tape readers for the program, with the transfer
from one to another being conditional, sort of like a conditional
subroutine call. Another addition allows the provision of plugboard-wired
subroutines callable from the tape.
Used to create ballistics tables for the US Navy.