MARIE, Day 01
The Components of the CPU
The CPU and memory are
components of a computer system. However, since they work so
closely together, it makes sense to discuss them at the same time.
The "brain" of the computer is the
Central Processing Unit
. On most of today's personal
computer systems, the CPU is called a Core and is made by Intel.
The Apple II used a 6502 8-bit processor.
The IBM PC used an 8086 (followed by an 80286, 80386, 80486, and the many variations of the
The Macintosh originally used a 68000 16-bit processor, followed by a PowerPC processor, and is
now using Intel's Core processors.
The two components of the CPU are the arithmetic-logic unit (ALU) (called the
by Null) and the
The ALU does the addition, subtraction, multiplication, and division and also some other
operations, such as logical ANDs, logical ORs, complementing, and shifting.
The Control Unit.
The control unit fetches, interprets, and controls the sequence of operations that must
be completed to carry out an instruction.
. The CPU has a number of memory locations for storing data. A memory location in the CPU is
A register may be either a special-purpose register or a general-purpose register. A general-purpose
register is available to the programmer to use as he wishes.
All data manipulation in a computer is done
on data in registers.
This means that before anything can be done to a data item, it must be copied from
memory into a register, then the data may be manipulated, then the result must be copied back to the
original memory location. Main memory is just that -- memory. It holds data until the data needs to be
manipulated, and it is used to store the result after it has been manipulated.