Overview of a computer system
Introduction
 This Unit explores the purpose of computer systems,
their structure and provides a technical description of
the components.
Overview of a computer system
Learning Objectives
 After studying this Unit, you will be able to:
 1. Describe the major functions of a general-purpose
computer system
 2. Explain the functions of the major hardware
components of a computer system
Overview of a computer system
 After studying this Session, you will be able:
 1. Explain the difference between a computer and a
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computer system
2. Describe the various components of a computer
3. List the different devices that are typically attached to a
computer to allow the user to input data and view output
4. Illustrate the components of the Central Processing Unit
(CPU)
5. Explain the function of the components of the Central
Processing Unit
Overview of a computer system
 Components of a Computer
 When you look at a desktop computer, it comprises:
 A monitor,
 Keyboard,
 Mouse, and
 A vertical or horizontal box called a system unit.
 It is acceptable to refer to all of these components as a
computer.
Overview of a computer system
 Components of a Computer
 Technically however, the system unit houses the actual
‘computer’
Overview of a computer system
 Components of a Computer
 Computer: An electronic programmable machine
which executes (carries out) or responds to a sequence
of program instructions
Overview of a computer system
 Components of a Computer
 A computer system is a collective term for a computer
(housed within the system unit), as well as these other
components that are attached to it to allow the user to
input data and view output using different devices.
Overview of a computer system
 Components of a Computer
 Some of these components include a monitor,
keyboard, mouse, printer, disk drives, scanners,
microphones, and speakers, which are also referred to
as peripherals.
 The peripherals work together to help the user
accomplish a given task effectively.
Overview of a computer system
 Components of a Computer
 The
peripheral devices mentioned above are
collectively called hardware devices, since they can
be physically attached to the computer.
 Hardware: The physical components that can be seen
and touched.
Overview of a computer system
 Components of a Computer
 computer systems also include software, or programs
that are integral in the functioning of some of these
peripheral devices and are necessary to make the
computer operate.
 Software: A set of instruction (programs) which tells
the computer what to do.
Overview of a computer system
 Components of a Computer
 Every computer system requires an operating
system.
 An operating system is a program that establishes
communications with the various peripherals and acts
as a bridge to other application (specific) software
programs.
Overview of a computer system
 Components of a Computer
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An operating system is like the command centre of
the ship.
 It makes all of the decisions about how the computer
will function and work with others.
Overview of a computer system
 Functions of the major hardware components of a
computer system
 The major components of a computer system include
input and output devices as well the important
processor or Central Processing Unit (CPU).
Overview of a computer system
 Functions of the major hardware components of a
computer system
 The CPU is the brain of a computer system and is
responsible for processing the data that is input from a
peripheral device and output to another peripheral
device.
Overview of a computer system
 Functions of the major hardware components of a
computer system
 The major components of a computer system include
input and output devices as well the important
processor or central processing unit (CPU)
Overview of a computer system
 The CPU comprises a set of electronic circuits kept
within the system unit.
 The CPU is the brain of a computer system and is
responsible for processing the data that is input from a
peripheral device and output to another peripheral
device
Overview of a computer system
The sketch above illustrates the major components of a
computer system.
Overview of a computer system
The Figure illustrates the components of the CPU along with
the other components of a system unit attached to an input
and output device.
Overview of a computer system
 The Central Processing Unit (CPU), also known as the
processor or microprocessor has components that
control the operating system and other software
installed on the computer.
 The CPU also sends commands and data to the
peripherals attached to the computer, such as the
monitor or printer.
Overview of a computer system
Overview of a computer system
 Now let’s look into the operation of the CPU.
 All computer systems have a CPU which comprises:
 1. a Control Unit (CU) and
 2. an Arithmetic and Logic Unit (ALU).
Overview of a computer system
 The Control Unit (CU)
 The control unit is similar to an efficient manager or
traffic cop.
 It is responsible for directing other parts of the
computer system in order to carry out the instructions
for the task required.
 The control unit (CU) must interact with the
arithmetic and logic unit (ALU) and memory to
complete its tasks.
Overview of a computer system
 The Control Unit (CU)
 The CU interprets the instruction.
 The CU then sends commands to other components
to gather data that may be needed to complete the
instruction, even if it involves a transfer of data from
other components and devices.
 The CU than determines where to send the result.
This may include activating the printer, showing the
result on the monitor or playing a sound on the
speakers.
Overview of a computer system
 Arithmetic and Logic Unit (ALU)
 The Arithmetic and Logic Unit (ALU) is the part of the
CPU which performs all arithmetic and logic
operations, this involves arithmetic calculations
including addition, subtraction and multiplication.
Overview of a computer system
 Arithmetic and Logic Unit (ALU)
 As calculations are required, the Control Unit sends
them to be performed in the ALU which sends the
result back to the Control Unit.
 It also performs logic operations such as comparisons
of numbers or letters to test for, such as equal-to (=),
less-than (<), greater- than (>) and other
combinations, such as less-than or equal-to (<=).