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The central processing unit(CPU).
The brain of any computer system is the CPU. It controls the functioning of the other
units and process the data. The CPU is sometimes called the processor, or in the personal
computer field called “microprocessor”. It is a single integrated circuit that contains all the
electronics needed to execute a program. The processor calculates (add, multiplies and so
on), performs logical operations (compares numbers and make decisions), and controls the
transfer of data among devices.
The processor acts as the controller of all actions or services provided by the system.
Processor actions are synchronized to its clock input. A clock signal consists of clock cycles.
The time to complete a clock cycle is called the clock period. Normally, we use the clock
frequency, which is the inverse of the clock period, to specify the clock. The clock frequency
is measured in Hertz, which represents one cycle/second. Hertz is abbreviated as Hz.
Usually, we use mega Hertz (MHz) and giga Hertz (GHz) as in 1.8 GHz Pentium. The
processor can be thought of as executing the following cycle forever:
1. Fetch an instruction from the memory,
2. Decode the instruction (i.e., determine the instruction type),
3. Execute the instruction (i.e., perform the action specified by the instruction).
Execution of an instruction involves fetching any required operands, performing the
specified operation, and writing the results back. This process is often referred to as the fetch-
execute cycle, or simply the execution cycle. The execution cycle is repeated as long as there
are more instructions to execute. This raises several questions. Who provides the instructions
to the processor? Who places these instructions in the main memory? How does the processor
know where in memory these instructions are located?
Lec. (8)
Computer Fundamentals
1'stage
College of Computer Technology
Dept.Information Networks
