The document discusses the components and functional units of a basic computer system. It describes the input, storage, processing, control, and output units. The central processing unit (CPU) processes data and includes the arithmetic logic unit (ALU) and control unit (CU). Storage units include primary storage like RAM and ROM, and secondary storage devices like hard disks, floppy disks, CDs, DVDs, and magnetic tapes that allow for permanent storage of data and programs.

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Lesson 2:
COMPONENTS
OF A
COMPUTER SYSTEM

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Computer SystemComputer System
A computer system consists of mainly four
basic units: input unit, storage unit, central
processing unit and output unit.
Central Processing unit further includes
Arithmetic logic unit (ALU) and control unit
(CU)

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A computer performs five major
operations or functions:
• it accepts data or instructions as input,
• it stores data and instruction
• it processes data as per the
instructions,
• it controls all operations inside a
computer
• it gives results in the form of output.
Computer System.. contComputer System.. cont

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Basic Computer SystemBasic Computer System
OrganizationOrganization
CPU
ALU
MEMORY UNIT
CU
INPUT OUTPUT
STORAGE

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Functional Units:
1.Input Unit. This unit is used for entering
data and programs into the computer system by
the user for processing.
2. Storage Unit. The storage unit is used for
storing data and instructions before and after
processing.
3.Output Unit. The output unit is used for
storing the result as output produced by the
computer after processing.

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4. Processing. The task of performing
operations like arithmetic and logical operations
is called processing.
The Central Processing Unit (CPU)
takes data and instructions from the storage unit
and makes all sorts of calculations based on the
instructions given and the type of data provided.
It is then sent back to the storage unit. CPU
includes Arithmetic logic unit (ALU) and control
unit (CU)

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Functional Units… cont.
• Control Unit - controls all operations
like input, processing and output.
-It takes care of step by step processing of all
operations in side the computer.
•Arithmetic Logic Unit- all calculations and
comparisons, based on the instructions provided,
are carried out.
- it performs arithmetic functions like addition,
subtraction, multiplication, division and also
logical operations like greater than, less than
equal to, and etc.

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The Central Processing Unit (CPU)
takes data and instructions from the
storage unit and makes all sorts of
calculations based on the instructions
given and the type of data provided.
It is then sent back to the storage
unit. CPU includes Arithmetic logic
unit (ALU) and control unit (CU)

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Functional Units… cont.
5. Primary and
Secondary Storage
a. primary storage
a.1 RAM
a.2 ROM
b. secondary storage
b.1. magnetic disk
b.2. magnetic tape
b.3. optical disk
b.4. punched card
.

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Functional Units… cont.
a. Primary Storage
a.1. RAM or Random Access Memory
- It is the place in a computer where the
operating system, application programs
and the data in current use are kept
temporarily so that they can be accessed
by the computer’s processor.

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Functional Units… cont.
a. Primary Storage
a.1. RAM or Random Access Memory
- It is said to be ‘volatile’ since its contents
are accessible only as long as the
computer is on. The contents of RAM
are no more available once the
computer is turned off
•

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Functional Units… cont.
a. Primary Storage
a.2. ROM or Read Only Memory
-is a special type of memory which can only be
read and contents of which are not lost even
when the computer is switched off.

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Functional Units… cont.
a. Primary Storage
a.2. ROM or Read Only Memory
-It typically contains manufacturer’s instructions.
Among other things, ROM also stores an initial
program called the ‘bootstrap loader’ whose
function is to start the operation of computer
system once the
power is turned on.

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Functional Units… cont.
b. Secondary Storage
- devices and peripherals that are
connected and controlled by the computer to
enable permanent storage of programs and
data.
e.g. Magnetic disks and optical disks

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Functional Units… cont.
b. Secondary Storage
b.1. Magnetic disks
b.1.1. Hard Disk - made up of rigid material and
are usually a stack of metal disks sealed in a
box.
- the hard disk and the hard
disk drive exist together
as a unit and is a
permanent part of the
computer where data
and programs are saved.

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Functional Units… cont.
b. Secondary Storage
b.1. Magnetic disks
b.1.1. Hard Disk - these disks have
storage capacities ranging from 1GB to
80 GB and more.
- rewritable.

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Functional Units… cont.
b. Secondary Storage
b.1. Magnetic disks
b.1.3. Floppy disk - a disk
storage medium composed of a disk of thin
and flexible magnetic storage medium,
sealed in a rectangular plastic carrier lined
with fabric that removes dust particles.

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Functional Units… cont.
b. Secondary Storage
b.1. Magnetic disks
b.1.3. Floppy disk - floppy disks are read
and written by a floppy disk drive (FDD).
- floppy disks, initially as
8-inch media (360 KB) and later in 5¼-inch (1.2
MB) and 3½-inch (1.44 MB) sizes, were a
ubiquitous form of data
storage.

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Functional Units… cont.
b. Secondary Storage
b.2. Optical disks
b.2.1. Compact Disk (CD) - a portable
disk having data storage
capacity between 650-
700 MB.
- It can hold
large amount of information
such as music, full-motion videos, and
text etc.
- CDs can be
either read only or read write type.

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Functional Units… cont.
b. Secondary Storage
b.2. Optical disks
b.2.2. Digital Video Disk (DVD) - is
similar to a CD but has larger storage
capacity and enormous clarity (high
video and sound quality).
- can store several
Gigabytes of data.
- DVDs are primarily
used to store music or movies and can
be played back on your television or the
computer too.
- not rewritable.

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Functional Units… cont.
b. Secondary Storage
b.2. Optical disks
b.2.3. Blu-ray Disc (BD) - designed to
supersede the DVD format
- capable of storing high-
definition video resolution (1080p)
- contain 25 GB per layer, with
dual layer discs (50 GB) being the
industry standard for feature-length video
discs. Triple layer discs (100 GB) and
quadruple layers (128 GB) are available
for BD-XL re-writer drives

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Functional Units… cont.
b. Secondary Storage
b.2. Optical disks
b.2.3. Blu-ray Disc (BD)
- the name Blu-ray Disc refers
to the blue laser used to read the disc,
which allows information to be stored at a
greater density than is possible with the
longer-wavelength red laser used
for DVDs.

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Functional Units… cont.
b. Secondary Storage
b.2. Optical disks
b.2.3. Blu-ray Disc (BD)
- the major application of Blu-
ray Discs is as a medium for video
material such as feature films and
physical distribution of video games for
the PlayStation 3
and 4, and Xbox
One.

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Functional Units… cont.
b. Secondary Storage
b.2. Optical disks
b.2.3. Blu-ray Disc (BD)
- associated with a set of
multimedia formats.
- these formats allow for the
option of video and audio to be stored
with greater definition than on DVD.

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Functional Units… cont.
b. Secondary Storage
b.3. Magnetic tapes
b.3.1. Magnetic tape data storage
- is a system for storing digital
information on magnetic
tape using digital
recording.
- modern magnetic tape is most
commonly packaged
in cartridges and cassettes.

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Functional Units… cont.
6. Other Storage Devices
6.1. Secondary Storage
b.3. Paper Medium
b.3.1. Punched Cards
- punched card, punch
card, IBM card, or Hollerith card
- a piece of stiff paper that
contained either commands for
controlling automated machinery or data
for data processing applications.

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Functional Units… cont.
6. Other Storage Devices
6.1. Secondary Storage
b.3. Paper Medium
b.3.1. Punched Cards
- both commands and
data were represented by
the presence or
absence of holes
in predefined positions.

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Functional Units… cont.
6. Other Storage Devices
6.1. Secondary Storage
6.1.1. Pen drive - flash memory with an
integrated Universal Serial Bus (USB)
interface.
- flash drives are typically removable and
rewritable, and physically much smaller
than any secondary storage.
- faster, have thousands of times more
capacity, and are more durable and
reliable because they have no moving
parts.
- immune to magnetic interference (unlike
floppy disks), and unharmed by surface

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- faster, have thousands of times more
capacity, and are more durable and
reliable because they have no
moving parts.
- immune to magnetic interference
(unlike floppy disks), and unharmed
by surface scratches (unlike CDs).

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Functional Units… cont.
6. Other Storage Devices
6.1. Secondary Storage
6.1.2. Pen drive - smaller, faster, have
thousands of times more capacity, and are
more durable and reliable because they
have no moving parts.
- immune to magnetic interference
(unlike floppy disks), and unharmed by
surface scratches (unlike CDs).