central processing unit (CPU): the computer nerve center, coordinates and
controls the activities of all the other components, performs arithmetical and
logical processes to be applied to data, and stores data.
b. The Arithmetic/Logic Unit. The arithmetic/logic unit (ALU) performs the four
arithmetic operations (addition, subtraction, multiplication, and division) which are, in
turn, used to perform logical operations. An example of a logical operation might be
comparing one data item to another to see which is less. Since the bulk of internal
processing involves calculations or comparisons, the capabilities of a computer often
depend on the design and capabilities of the ALU.
c. The Primary Storage Unit. Also known as the internal storage, core
memory, or main storage, this is a temporary storage. It stores the program and data,
for immediate use, while they are being worked with. The program and data are
inserted into the storage area, often called the memory, through the input unit. While
the computer is solving a problem, the program instructions and data continually run
back and forth between the arithmetic/ logic unit, the control unit, and the storage unit.
Magnetic core storage system.
(a) The information stored in the core memory or main storage is
stored in a series of "cubbyholes." Each cubbyhole (location) has an address. The
information at the address consists of binary digits or bits stored by an ingenious system
of magnetized "doughnuts" suspended on a wire network.
bit: short for binary digit; the smallest unit of information recognizable to a
Figure 2-5. The central processing unit (CPU).
(b) The magnetism in the magnetic core is induced by a current in the
wire network (clockwise magnetism representing a 1 bit and counterclockwise
magnetism, a 0 bit). The direction can be sensed when the information needs to be
read. The 1 or 0 bit is the part of the electronic code that the computer uses to process
letters, numerals, or symbols, and the bits are grouped to form a particular code for
each letter or numeral.