b. Features of Electromechanical Punch Card Machines. Electromechanical
devices used electrical power to provide mechanical motion to do such things as turn
the wheels of an adding machine. Such systems could automatically feed in a specified
number of cards from a "read-in' station. They could also add, multiply, and sort and
feed out cards with punched results. By modern standards, the punch card machines
were slow, processing 50 to 250 cards per minute, with each card holding up to 80
decimal numbers. And the need for manual intervention between processing stages
was a major drawback. But, nonetheless, punch cards marked a significant step
forward, providing a means of input, output, and memory storage on a massive scale.
electromechanical: composed of electrical and mechanical parts.
1-14. PUNCH CARD EQUIPMENT VS LATER COMPUTERS
Punch card equipment was effective in performing many of the individual steps
necessary to process data, e.g., sorting, calculating, and summarizing. But it still
required people to handle trays of cards between each step. Separate machines had to
be fed, started, and stopped. The limited intercommunication between processing
stages and the need for manual intervention are the major disadvantages of punch card
equipment. Ultimately, with modern computers, manual interference between data input
and information output would be eliminated. Alterable instructions directing the machine
to perform automatically would be stored within the machine itself.
computer: any automatic device capable of performing calculations without
1-15. AIKEN'S MARK I AUTOMATIC DIGITAL COMPUTER (1937-1944)
a. Introduction. In 1944, Howard Aiken of Harvard University completed the
Mark I automatic digital computer, the first in a series of automatic calculating machines
that he built. The Mark I combined established technology with Hollerith's punch card
techniques. Besides arithmetic operations, these new machines had special built-in
programs or subroutines to handle logarithms and trigonometric functions. In a sense,
this was the realization of Babbage's unrealized Analytical Engine (though Aiken was
unaware of Babbage's work until the Mark I was near completion).
program: a sequence of detailed instructions for performing an operation on a
problem by computer.
routine: ordered set of general instructions.
subroutine: a routine that can be part of another routine or program.