The document describes the components of a computer system, emphasizing hardware and software, with a focus on various types of input and output devices, the CPU, and memory configurations. It elaborates on the roles of input devices like keyboards and mice, the CPU's functions, and distinctions between primary and secondary storage types. Additionally, it addresses factors affecting computer speed, including memory amount, processor speed, and bus speed.

1. COMPUTER
SYSTEM
UNIT TWO
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2. Computer system
 It is a system which has its own goal and different interrelated
component that work together for the achievement of common
goals.
It has two main categories
1.Hardware
2.Software
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3. computer hardware
 Is the physical parts of the computer; the parts that you can see
and touch.
 It can broadly be divided into:
 Input Devices
 CPU/processer
 Memory / Storage Devices
 Output Devices
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4. Input devices
 It lets us communicate with a computer.
 They are devices used to supply input (data/ instruction) to the
processing unit.
 There are different types of input devices.
 They differ in
 size
 data input method
 format of data entry, etc.
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5. some of the major input devices are:
 Pointing Devices ,
 A keyboard,
 scanner,
 digital camera,
 Microphone and
 Video Capture Card .
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6. Pointing Devices
 It move some object on the screen and can do some action
 Common pointing devices
 Mouse - most common pointing device
 Trackball has the ball on top and you move it with your finger.
 Touchpad allows you to move your finger across a pressure
sensitive pad and press to click.
 Joystick - consists of a handheld stick
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7. Keyboard
 Used to type data into the computer
 The standard keyboard contains 83 keys.
 Recent machines used enhanced keyboard that has up to 105 key.
 On modern key boards there are four major groups of keys
 Function keys usually labeled F1-F12 are used as command buttons for
applications. E.g. F1=HELP F5=REFREASH
 The type writer or alpha numeric keys are the alphabets a to z and the
numbers 0 to 9.
 Numeric key contains numbers, arithmetic operations and cursor movement
keys.
 Special keys include delete, shift, enter, end, control, alt, etc.
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8. Scanner
 It allows us to scan documents, pictures, or graphics and view
them on the computer.
 You can also use software to edit the items you scan.
 Used to put printed pictures and text into a computer
 Converts an image into dots that the computer can understand
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9. Digital Camera
 Used to take electronic pictures of an object
 The pictures taken by a digital camera can be used directly by a
computer
Microphone
 Used to put sound into a computer
 Need sound recording software
 Convert speech (analog s.) to digital form
Video Capture Card
 Use to put video into a computer
 Need a video source, either a video camera or video recorder
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10. The Processor/CPU
 It is a place where every activity of computer system is hold.
 Is considered as brain of computer.
 All the other components RAM, disk drives, the monitor exist
only to bridge the gap between you and the processor.
 Special processors such as that inside the key board also exist to
handle the signal generated whenever you press a key and
releases key.
 The current standard is an Intel Pentium micro processor chip.
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11. The CPU has three components
 The arithmetic logic unit (ALU)
 The control unit (CU)
 The registers
 ALU:
 is the place where the actual execution of the instructions takes place during
data processing operation.
 Is a place where the arithmetic operation and logical operation takes place.
 That is, when the control unit encounters an instruction that involves an
arithmetic operation (such as add, subtract, multiply divide) or a logical
operation (such as less than, equal to, greater than), it passes control to the
CPU.
11

12. Cont.…
 CU:
selects and interprets program instructions and then sees that
they are executed.
It doesn’t perform any actual processing on the data,
It manages and coordinates the entire computer system
including the input and out put units.
It obtains instructions from the program stored in the main
memory, interrupts the instruction, and issues signals that cause
other units of the system to execute.
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13. Cont.…..
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Registers:
 registers are temporary, high speed storage elements inside CPU.
 The length of a register equals the number of bits that it can
store. Thus a register that can store 8 bits is normally refereed to
as an 8 bit register.
 Most CPUs sold today have 32 bit or 64 bit register.

14. Memory
 The system memory is the place where the computer holds programs
and data that are in use.
 The capacity of a storage device is mostly measured in bytes. Other
measurements include:
 Kilo byte (KB) =210 bytes which is equal to 1024 characters.
 Megabyte (MB) = 220 bytes
 Gigabyte (GB)=230 bytes
 The two most important types of memory are:
 Primary memory
 Secondary memory
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15. Primary storage
 Presently known as memory.
 It is the only one directly accessible to the CPU.
 It is directly or indirectly connected to the CPU via BUS.
 It is much faster to access than secondary storage because of the
proximity of the storage to the processor.
 It can be divided into two essential types:
RAM
ROM
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16. Random access memory (RAM)
 It is temporary and volatile.
 It is a computer workspace where data and instruction for
immediate processing are held.
 It is the working area of the computer.
 It is dependent on the power supply.
 When first switched on RAM is empty until a program is loaded
into it.
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17. Read-only-memory (ROM)
 It is permanent
 Booting starts on ROM because it holds special program or
instructions
 POST (Power on Self Test) to make sure all its components are
working properly and to warn you if something is missed.
 It can’t be changed by the computer user.
 If ROM is damaged, the computer system simply can’t function.
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18. Secondary Storage device
 It is also called secondary memory or storage.
 It is not directly accessible by the CPU.
 It can save data, information, and programs for long periods of
time.
 It also can keep them even when the computer is turned off or
unplugged.
 The main types of secondary memory are categorized in to
 magnetic storage devices.
 optical storage devices
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19. Magnetic storage
 Use the principle of magnetism.
 It is non-volatile.
 Magnetic storage will take these forms:
 Magnetic disk
 Floppy disk
 Hard disk
 Magnetic tape used for back up purpose
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20. Optical Devices:
 It uses the principle of laser technology to store data on a hard plastic disk.
 It has three types
 read only storage :
 CD, CD-ROMS, and DVD
 write once :
 CD-R, DVD-R, DVD+R
 Rewrite storage:
 CD-RW, DVD-RW, DVD+RW,
 Special DVD drives are necessary to read information from DVDs.
Fortunately, these drives also read CD-ROMs.
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21. Secondary storage characteristics
 Media ( actual physical material that holds the data and
programs, Example: CD).
 Capacity( measured how much a particular storage medium
can hold)
 Storage devices (are hardware that reads data and program
from storage media)
 Access speed ( measures the amount of time required by
storage device to retrieve data and program).
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22. Output devices
 Output devices display information in a way that you can
understand.
 They are devices that bring information out of a computer.
 Common output formats are
 printed-paper,
 sound,
 video and
 on-screen documents.
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23. Some of the major output devices are:
 Monitors
 Printers
 Plotters
 Speakers
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24. Monitors or Visual Display Units (VDUs):
 It looks a lot a like a TV.
 It produce Soft copy output.
 It allows you to 'see' what you and the computer are doing together.
 It is a device that displays a video signal, similar to a television.
 These are the most common types of Monitors :
Desktop monitors which are also known as Cathode Ray Tube
(CRT)
Liquid Crystal Displays (LCD) which are also known as Thin
Film Transistors (TFT)
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25. Printers
 a peripheral device that produces a hard (usually paper) copy of a
document.
 It takes what you see on the computer screen and prints it on paper.
 There are three types of printers.
 Laser printers: use lasers to print.
 Produce a very high quality output, are very quiet and very fast.
Laser color printers are quite expensive to buy.
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26. Cont.…
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 Ink-jet printers: uses inks to print.
 Offer black and white or color printing with reduced levels of
quality and speed. Color ink jet printers are cheaper to buy than
color laser printers.
 Dot-matrix printers: use hammer to print.
They are comparatively noisy and low quality but are cheap.

27. Plotters
 A plotter can be used to produce high quality, accurate, A3 size or
bigger drawings.
 They are usually used for printing out plans for houses or car
parts.
Speakers
 It allow you to hear sound from your computer.
 It is a device that converts analog audio signals into the
equivalent air vibrations or digital signal in order to make audible
sound.
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28. Factors Affecting a Computer’s Speed
Amount of memory (RAM)
 The more RAM a computer has, the more program instructions and data can be
held in memory
 If a computer does not have enough memory to run a program, it must move data
between RAM and the hard disk frequently.
Processor Speed
 Processor speed represents the number of instructions it can execute per sec.
 The faster a computer's processor is, the more instructions the computer can
execute each second.
 A processor’s speed is measured in Hertz, MHz and GHz .
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29. Cont.….
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Bus Speed
 A bus is a path between the components of a computer.
 Data and instructions travel along these paths.
 The data bus' speed determines how many bits can be
transmitted per second between the CPU and other devices

30. END OF UNIT
TWO
.
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