How did it work?



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Mark I worked around the clock on military projects, calculating massive mathematical tables. Principallyit helped the Navy by computing tables for the design of equipment such as torpedos and underwater detection systems. Other branches of the military sought its help in calculating the design of surveillance camera lenses, radar, and implosion devices for the atomic bomb in the Manhattan Project.

The mathematical tables that Mark I churned out were the first of their kind: They were printed directly from a machine’s output, eliminating all human error. One of the computer’s longest running projects required it to solve a set of differential equations called Bessel Functions. As a result, the computer was given the nickname “Bessie.”

Howard Aiken emphasized the unequaled reliability and precision of calculation of Mark I, even if it was hundreds of times slower than would have been possible with vacuum tubes. Through its sturdiness and precise performance, Mark I was able to work practically uninterrupted for 16 years.



Functional Components



     Tap each number to learn more about each portion of the machine.


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Constant Switches

These dials were used to enter numbers. They were set up before running a program and remained unaltered until the end of a problem run. Each row has space for one 24-digit number.
Storage Counters

Each of the original 72 units was a modified, mechanical adding machine of IBM design. Acting as the machine’s memory, they were read and operated according to instructions on the sequence tape.
Sequence Control and Interpolators

These were Howard Aiken’s main contribution, which made Mark I programmable. The sequence control read instructions to Mark I from a paper tape, taking in one line at a time, and executing the corresponding instruction in one step.

Interpolators were similar units set up to read sequences of numbers and mathematical functions, encoded in three lines of instruction.
Drive Shaft

Mark I was powered by an electrical motor that transmitted motion to all its mechanical components through a single long axle. This guaranteed that all its components worked at the same pace, which was necessary to transmit instructions and data among them as a single working unit.
Card Feeds, Card Punch

Card feeds were used to input problems encoded in standard punch cards of the period. The output could also be in punch card format, or in directly readable numbers keyed by the typewriters.

All this equipment was standard IBM stock, disguised behind Mark I’s futuristic outer case.
Constant Switches

These dials were used to enter numbers. They were set up before running a program and remained unaltered until the end of a problem run. Each row has space for one 24-digit number.
Storage Counters

Each of the original 72 units was a modified, mechanical adding machine of IBM design. Acting as the machine’s memory, they were read and operated according to instructions on the sequence tape.
Sequence Control and Interpolators

These were Howard Aiken’s main contribution, which made Mark I programmable. The sequence control read instructions to Mark I from a paper tape, taking in one line at a time, and executing the corresponding instruction in one step.

Interpolators were similar units set up to read sequences of numbers and mathematical functions, encoded in three lines of instruction.
Drive Shaft

Mark I was powered by an electrical motor that transmitted motion to all its mechanical components through a single long axle. This guaranteed that all its components worked at the same pace, which was necessary to transmit instructions and data among them as a single working unit.
Card Feeds, Card Punch

Card feeds were used to input problems encoded in standard punch cards of the period. The output could also be in punch card format, or in directly readable numbers keyed by the typewriters.

All this equipment was standard IBM stock, disguised behind Mark I’s futuristic outer case.




 
Collection of Historical Scientific Instruments   © President and Fellows of Harvard College