•The CPU, for
central processing unit, is the “brain” of the computer; it
follows the instructions of the software (program) to manipulate data into
information.
•The CPU
consists of two parts—(1) the control
unit and (2) the arithmetic/logic unit (ALU), both of which
contain registers,
or high-speed storage areas.
•All are
linked by a kind
of electronic “roadway” called a bus.
•For every instruction, the control
unit carries out four basic operations, known as the
machine cycle. In the machine cycle, the
CPU (1) fetches an instruction, (2) decodes
the instruction, (3) executes the
instruction, and (4) stores the result
•The arithmetic/logic
unit (ALU) performs arithmetic operations and
logical operations and controls the speed of those operations.
•Arithmetic
operations
are the fundamental math
operations: addition, subtraction, multiplication, and division.
•Logical
operations are comparisons--the
ALU compares two pieces of data to see whether
one is equal to ( = ),
greater than (>), greater than or equal to ( >= ),
less than (<), less than or equal to ( <= ),
or not equal to ( ≠
) the other.
•The control unit and the ALU also
use registers,
special CPU areas that enhance the computer’s
performance.
•Registers are high-speed storage areas that
temporarily store data during processing. They
may store a
program instruction while it is being decoded,
store data while it is being
processed by
the ALU, or store the results of a calculation.
•All data must be represented in a
register before it can be processed.
•The number of registers that a CPU
has and the size of each (number of bits) help
determine the power and speed of a CPU.
•Buses are electrical data “roadways”
through which bits are transmitted within the CPU
and between the CPU and other
components of the motherboard.
•In most computers, the bus width is
the same as the computer’s word size, the number of
bits that the
processor can process at any one time. The more bits in a word, usually the
faster the computer. A 32-bit-word computer will transfer data within each
microprocessor
chip in 32-bit chunks. A 64-bit-word computer is faster, transferring
data in 64-bit chunks at
a time. (Most, but not all, 32-bit software will run
on a 64-bit system, but 64-bit software will
not run on a 32-bit system.)
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