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Central Processing Unit
Central Processing Unit
The computer processor, often called the Central Processing Unit (CPU), is the circuitry that execute the program
instructions to process data. It consists of the Control Unit
and the Arithmetic Logic Unit that are connected by an electronic
roadway called a bus. The processor work with main memory (RAM) and
registers to turn data into information.
The functions performed by each part of the CPU follows.
- Control Unit. This unit directs and coordinate processing. The control unit sequentially
retrieve instructions from RAM and places them into an instruction
register. Each instruction is then interpreted to find out what need to be
done. According to the interpretation, the control unit then sends signal
to the data bus to fetch data from RAM, and to the ALU to process the
data.
- Arithmetic Logic Unit. This unit perform arithmetic and logical operations such as
addition, subtraction, and comparisons. The ALU contain the circuitry that
perform additions and comparisons plus temporary storage areas called registers
and accumulator. The registers hold data that
is being processed. The accumulator hold the result of an
arithmetic or logical operation.
The Machine Cycle
The machine cycle comprises a series of operations performed
to execute a single program instruction. The time required to complete the
cycle is dependent on processor speed, which is measured by the system clock
rate. The machine cycle consist of two parts: an instruction cycle,
which fetches and decodes, and an execution cycle which executes
and stores.
Instruction
Set
A computer perform a complex task by
performing a series of very simple steps, that are referred to as
instructions. The list of instructions that a CPU can perform is known by
the instruction set.
The following example illustrate
how the CPU process instructions.
Performance
Computer
performance are affected by the following factors:
- RAM Capacity
- Processing Speed
- For microcomputers is measured by the system
clock. For example, a 500MHZ processor means a system clock
rate of 500 million tick per second.
- For Mid-Size Computers and Mainframes is
measured by millions of instructions per seconds (MIPS).
- For Supercomputers is measured by
floating points operations per second (flops)
- Word Size refer to the number of bits the processor
can hold in its registers and transfer over the bus at one time.
- Instruction Set
- Complex Instruction Set Computer (CSIC)
- Reduced Instruction Set Computer (RISC)
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