Manual for the Atanasoff-Berry Computer

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COUNTERS    In all computing machines there is a counter of some sort
which represents or remembers numbers by virtue of the various states which
its parts may assume. In this machine the role of counter is played by a
set of electrical condensers, each of which corresponds to one place in
a number to the binary or base-2 system. The term counter will be extended
to include such a set of condensers.
The two digits, 1 and 0, of the base-2 system are represented respectively
by negative and positive charges on the contacts connected to the condensers
of a counter. Referring to Fig. 1, the condnesers 1 are mounted on the
interior of a cylinder 2 made of insulating material, with their inner ends
connected in common 3 and brought out to a slip ring 4, and their outer ends
connected to individual contacts 5 which protude through the walls of the
cylinder. The cylinder is arranged to be rotated at constant speed past
a pair of brushes 6, ? (Fig. 2) which are spaced half the distance between
contacts. The first brush 6 to touch a given contact is called a "reading"
brush, and the second 7 is called a "charging" brush. Fig. 6 gives an
assembly view of the entire set of brushes for the computing counter and
Fig. 5 gives the assembly view of the holder-shifter counter (defined later).
A portion 8 (Fig. l) of the periphery of a counter is left free of contacts
in order that during the period of a complete revolution of a counter there
will be a-certain amount of time available for resetting various parts of
the machine.
Counters are used for two main purposes in this machine—the first,
merely to hold a number as long as desired so that it may be used over and
over again in a computation; and the second, to retain instantaneous results
of computation (this might be called an accumulator). For certain operations
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