Hardware Components of a Computer
A computer system consists of the physical computer, called
the hardware, and the programs, called the software,
that instruct the machine. The term architecture refers to
the way the computer hardware is organized. There are several
variations but basically the computer hardware is organized into five
functional components. This organization is much the same as the
organization outlined by John von Neumann over 50 years ago and is often
called the von Neumann architecture.
The Five Hardware Components of a Computer
- Central Processing Unit: This is the hardware
component in charge of processing instructions. It consists
of two parts:
- Control Unit (Controller) The Control Unit
is in charge of (oversees) the execution of intructions. For
each instruction, it must "fetch" the instruction from main memory,
"decode" it (figure out what it says to do), then send signals to the
unit of the computer that will do the actual execution of
the instruction. There are two small memory locations (called
registers) in the Control Unit that are used to keep track of
things. These are
The decoding step is done by a circuit called the Instruction
The sequence of steps the Control Unit goes through as it
"controls" the execution of instructions is called
the fetch-execute cycle.
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- The Program Counter which contains the address
of the next instruction to be executed and
- the Instruction Register which contains the instruction
currently being executed.
- Arithmetic Logic Unit (ALU) The ALU is responsible
for performing arithmetic operations such as addition and multiplication
and logic operations such as the comparison of two numbers.
In personal computers, the circuits that make up the CPU are
all on a single silicon chip called the microprocessor.
Check out the
techweb.com Web site for more information about microprocessor chips.
The link takes you to an encyclopedia. Look up the word microprocessor
to see the insides of a microprocessor and the word chip to
see more information about chips in general (including their history
and an explanation
of how they are made).
- Main Memory Main memory is for the storage of instructions
and data currently being used by the CPU; that is, it is the
working memory of the computer. Most of main memory consists of
Random Access Memory (RAM) though a small portion is Read Only Memory (ROM).
ROM is a permanent, unchangeable (it can only be "read" from not
"written" to) part of main memory that contains among other things
the instructions that start the process of booting the machine (loading
the operating system). RAM, on the other hand, is much larger and
changes constantly as the CPU does its work. RAM is volatile, meaning
that all data is lost when the power is off; ROM is not volatile.
Main memory consists of a sequence of storage locations (cells) each
with its own address.
- Auxiliary Memory Auxiliary memory is for long term storage
of instructions and data. Magnetic disks are currently the most common
type of auxiliary memory. Programs and data must be "saved" to
auxiliary memory and "retrieved" or "opened" before they can be used
- Input Devices Input devices are for the user to communicate
with the computer by entering data (including programs) or issuing
commands. Common input devices are the keyboard and
- Output Devices Output devices are for the computer to
communicate with the user. Common output devices are the monitor,
printer, and speakers.
The CPU and main memory are realized in chips mounted on a circuit
board called the motherboard or system board. The
different components are connected by a group of wires called a bus.
Data, instructions, and control signals travel along the bus as
the various components communicate with each other.
The above description gives a general overview of basic computer
hardware. There are many variations in modern computers designed
to speed the computer up. Many modern computers are multiprocessors; that
is, they have more than one CPU. Most modern computers have an
additional type of memory called cache. Cache is an
intermediate form of memory designed to speed up access to data. There
is RAM cache which is used to speed up the CPU's access to data
in RAM and disk cache which is used to speed up access to data on
A good Web site for looking up information about computer hardware
pctechguide.com. Check it out.