TOPIC 2: THE COMPUTER – COMPUTER FORM ONE NOTES

What is computer studies?

A computer study is a subject which deals with features of computers and the ways and methods of using it.

Objectives: –

This unit is intended to enable students to understand:

• The basic definition of a computer
• The meaning/definitions of important (key) words The main (basic) functions/ processes of the computer
• How a computer works
• Characteristics/features of a computer
• Advantages of a computer
• Applications (uses) of computer in different areas of human life Different types of computers.

What is a computer?

• Is an electronic machine that accepts data from an input device performs arithmetic and logical operations according to predefined program and finally transfers the processed data to any output device.
• An electronic machine that processes raw data to generate (produce) information.
• Is an electronic machine that receives (accepts) input (raw data), processes it, and then produces output (information)
• Is an electronic machine that can be programmed to accept data (input) and process it into useful information (output)
• Is an electronic machine (device) that works under the control of stored programs, automatically accepting and processing data to produce information.
• Is an electronic machine that operates (works) under the control of instructions(programs) stored in its main memory, that can accept data (input), manipulate the data according to specified rules (process), produce results or information (output), and store the results for future use.

A good definition of computer contains the basic functions of a computer i.e. input, process, Storage, Output.

A COMPUTER BLOCK DIAGRAM

BASIC FUNCTIONS OF A COMPUTER

INPUT: Is any data or instructions entered into a computer.

There are four types of input which are: (i) Data (ii) Programs (iii) Commands

(iv) User responses

STORAGE: Is the ability of a computer or an area in a computer to hold data instructions and information for future use.

Two types of computer storage are: (i) Main storage (main memory),

(ii) Backing storage

PROCESSING; in the activity of changing data into information.

OUTPUT: Is data that has been processed into a useful form called information.

Types of output:

The four common forms of output are:

• Text e.g. words, sentences, paragraphs.
• Graphics e.g. drawings, charts, photographs.
• Audio e.g. music, speech or any other sound. Video e.g. played back images.

COMMUNICATION: Is the sending and receiving of data and programs from one computer or secondary storage device to another.

HOW A COMPUTER WORKS

All digital computers work essentially the same way.

A human operator uses input equipment to enter data and instructions into the computer. The processor then performs manipulation on the data, while the memory stores information during processing. The results then are sent to the output equipment, which presents them to the user. File storage devices enable information to be saved for future use.

CHARACTERISTICS (FEATURES) OF A COMPUTER

It is very fast,

2. It is very accurate and reliable
3. It can work continuously without getting tired or bored.
4. It can work on and store large amounts of data items
5. It can solve any problem if a relevant set of instructions is input, (vi) It is able to access or recovers, retrieve large volumes of data.

(vii) It is able to communicate with other computer systems in a network.

ADVANTAGES AND DISADVANTAGES OF COMPUTER

(a) Advantages

• It works at a very high speed
• Its results are very accurate and reliable
• It can work continuously without getting tired or bored
• It can work on the stored large amounts of data items
• It can solve any problem if a relevant set of instructions is input, (computer never think, bad programs will also produce bad output GIGO —garbage in garbage out)
• It is flexible
• It reduces paper work significantly.
• It reduces number of employees in organizations. It uses a small office space It is automatic.
• It allows fast retrieval of information from a storage space.
• It can store information efficiently
• Computers can move information very quickly from one person to another.

(a) Disadvantage

• It is costly It becomes outdated very fast due rapid changes in computer technology, hence it leads to capital loss
• It causes loss of employment in certain fields.
• It can fail. Such failures can cause loss of life e.g in traffic control system.
• Too much work at the computer causes nerve injuries.
• Loss of employment
• Loss of secrets Eye damage
• Loss of data.

APPLICATIONS OF COMPUTER IN DIFFERENT AREAS OF HUMAN LIFE

IN EDUCATION

• To teach (give courses) in different subjects
• To give Computer Assisted Instructions (CAI)
• To give Computer Assisted Learning (CAL)
• To keep records
• As a reseach tool e.g. to analyse data from experiments To process records
• To assist in education management.
• To keep records of books and borrowers in a library.

MEDICINE (HEALTH)

• To assist in hospital administration
• To keep records of employee and patients
• To monitor conditions of patients e.g. temperature, heart-beats
• To help doctors to investigate illness (diagnosis) and prescribe treatments. To do medical research.

HOME

• For recreation e.g. playing games, listening to music
• As an education tool
• To store personal information
• To access to news when connected to the internet
• To access databases
• As a home accountant to keep a track of expenses and to balance a family budget
• To protect homes against crimes from burglary vandals by using electronics security systems. For alert emergence services automatically e.g fire brigade, police.

IN INDUSTRY AND ENGINEERING

• To design drawing for products using Computer Aided Design (CAD) programs e.g. airplanes, bridges, cars, buildings, electronic circuit boards.
• To manufacture products using Computer aided Manufacturing (CAM) To plan and control major projects.
• To simulate (predict what will happen in real-life situation from a model situation.) e.g. turning of traffic lights.
• To control some operations in automobiles e.g mixing of fuel and air entering the engine
• A branch of computer science called artificial intelligence, uses programs that help to solve problems by applying human knowledge and experience e.g. in medicine, law etc.

IN BANKING AND BUSINESS

• To allow bank clerks and customers to find out bank balances in an account
• To help bank clerks to record money paid in and out
• To check computer sensitive cheques, to do reservation system for airline travel by checking of there is a free seat on a flight.
• To help retailers to check out stock at a supermarket
• To control industrial robots
• To allow people to use Automatic Teller Machines (ATM) in cash withdraw and transfer funds between accounts.
• To keep track of current prices of market stocks, bonds currency.
• Creates an effective way of producing document e.g. reports, brochures, cards.

MILITARY

• It can be used for planing and decision — making
• It can used by planners to stimulate wars
• It can be used to guide modern weapons such as missiles and field artillery.

IN GOVERNMENT

• It can be used for internal revenue services e.g to provide reports for tax purposes.
• It can be used for planning, analysis, forecast, sampling, predictions etc.
• It can be used for weather forecasting , It can be used for Law enforcement

IN TRANSPORTATION

• It can be used for a Traffic control
• It can be used in driving stimulator
• It can be used for reservation systems
• Are embedded in aircraft to provide efficiency in flying.

COMPUTER HARDWARE

• Is a collection of machines (physical components or elements) which form a complete computer system.
• Is the actual machinery that makes up the computer system.
• Is the collection all physical pieces of equipment (elements) that makes up a computer system.
• Is a set of devices that accept data, processes them and displays them. Is the set of all pyhsical parts of the computer.

TYPES OF COMPUTER HARDWARE

COMPUTER HARDWARE is a composed of the following components/elements according to the functions of the computer:

• Input devices or input hardware
• Central processing unit (CPU) or processing hardware
• Output devices or Output hardware
• Secondary storage devices or storage hardware
• Communication devices or Communication hardware

	HARDWARE DEVICES	EXAMPLES
	Input hardware (Input devices)	Keyboard,scanner
	Processing hardware (Processin devices)	The control units,the main memory
	Output hardware(Output devices )	Printer, Monitor and plotter
	Storage hardware(secondary storage devices)	Hard diskF10ppy
	Computer communications hardware(Computer communications devices)	Modem-CRT and terminals

A BLOCK DIAGRAM FOR CLASSIFICATION OF COMPUTER HARDWARE COMPONENTS (DEVICES or ELEMENTS)

PERIPHERALS (OR PERIPHERAL DEVICES or PERIPHERAL HARDWARE)

PERIPHERAL

• Is a device that is located outside the central processing unit (CPU) but controlled by it.
• Is an attachment to a computer used mainly to feed unprocessed data into the computer and receive the output of processed information.
• Is the totality of facilities or equipments connected to the computer to assist it in satisfying its users.

DEVICES

• Is any machine, but particularly a computer peripheral e.g. printer Is a computer peripheral

There are two types of devices

1. AN ONLINE DEVICES— is a peripheral devices that is in use
2. AN OFFLINE DEVICES — is a peripheral that is not in use

A MEDIUM — Is a material in which data is stored on or data is output to e.g. printed paper.

Types (categories) of peripherals

There are five main types or categories of peripherals (or peripheral devices). These are:

Input devices

2. Output devices
3. Input/output devices (i.e. both input and output devices)
4. Backing storage (secondary storage devices
5. Communication devices

INPUT DEVICES (INPUT HARDWARE)

INPUT

• Is getting (to get) data into a computer system
• Is the data that is put into the computer system for processing
• Is any data or instructions which you enter into the memory of a computer.

TYPES OF INPUT

Four types of computer input are: I. Data

Il. Programs

111. Command,

IV. User responses

• DATA is a collection of unorganized (meaningless) facts, e.g. words, numbers, pictures, sound and videos.
• Is raw material to be processes by the computer.
• A PROGRAM is a series of instructions that tells the computer how to perform tasks which are necessary to process data into information.
• A COMMAND is an instruction given to a computer program.
• A USER RESPONSE is an instruction you issue to the computer by replying to question posed by a computer program.

E.g Computer question: Do you want to save the changes you have made’?

Uses response: YES

AN INPUT DEVICE

• Is any hardware component that allows you to enter data, programs, commands and user responses into a computer.
• Is a peripheral (peripheral device) which accepts data and send it into the corresponding processing unit (CPU)
• Is a peripheral (peripheral device) which accepts data in a form that a computer can use and sends the data to the central processing unit (CPU).
• Is a peripheral (peripheral device) which accept data from outside the computer system and transmits (sends) it to the central processing unit (CPU).

Examples of input devices;

Keyboard, mouse, Lightpen, Joystick, Scanner, Bar-code reader, PEWS terminal,Trackball, Touch pad, Pointing stick , pen(stylus)

CHARACTERISTICS OF INPUT DEVICES

The characteristics of input devices are as follows:-

1. They form an interface between the external environment and the computer

An interface is a hardware (and sometimes a software) that is used to connect two devices or systems in order to enable them to communicate.e.g. A modem

2. They’re located next to or outside the CPU. In other words, they are attached to the computer.
3. They can be off-line or on-line

FUNCTIONS OF INPUT DEVICES

The functions of input devices are as follows: (i) To accept data from the user into the computer system

2. To accept instructions from the users.
3. To accept commands for running or aborting or halting a program from the user.

OUTPUT DEVICE / OUTPUT HARDWARE

OUTPUT

• Is data that has been processed into meaning form called information.
• Is usable information
• Is raw input data that has been processed of the computer into information.

Some examples of output

• Words, numbers, sentences, paragraphs
• Drawings, charts and photographs
• Music synthetic speech
• Played back images

Types (categories or groups) of output

Two principal kinds of output are

Softcopy

(ii) Hardcopy

Soft copy

Is a material (data) shown on the display screen (monitor) or data that is in audio or voice form.

This kind of output is not tangible; it cannot be touched.

Hardcopy

Is printed copy (printout) on paper.

Examples of printouts (hardcopy output)

1. Text and graphics from printers
2. Film (including microfilm and microfiche)

Forms of output

Computers generate (produce) several forms of output. They are:

(i) Text e.g. words, sentences, charts and paragraphs (ii) Graphics e.g. drawing, charts and photographs

(iii) Audio e.g. music speech etc (iv) Video e.g. played back images

COMMUNICATIONS DEVICES

COMMUNICATIONS HARDWARE

COMMUNICATIONS:

• Is the process of sending and receiving data and programs from one computer to another or secondary storage device to another.
• Is the process of transmitting (or sending) data from one person to another or from one device to another.

Examples of communications devices

(i) Modem (ii) Multiplexor

A MODEM

-Is a device by which computers exchange information over telephone lines.

-Is a piece of hardware that converts (changes) digital signals into analog signal and vice versa.

COMPUTER COMMUNICATION

Is the transfer of information between computers.

DATA COMMUNICATION

Is the process of transmitting (or sending) data from one user to another or from one computer to another.

TELECOMMUNICATIONS

Is data communication over large distances.

SECONDARY STORAGE DEVICES / SECONDARY STORAGE MEDIA

A STORAGE MEDIUM/STORAGE DEVICE – is a physical material on which items (data, Instructions and information) are kept for future use e.g. disks.

Examples of secondary storage devices/ secondary storage media

• Floppy disk (diskette), magnetic diskette.
• Magnetic disk or hard disk
• Magnetic tape

Optical disks e.g. CD,CD-ROM WORM and DVD, DVD-ROM, DVD-RAM and rewritable optical disks (cailed floptical, magneto-optic)

Types of Primary storage and Secondary storage devices

Computer storage

CHARACTERISTICS OF SECONDARY STORAGE DEVICES

Secondary storage devices have a several common characteristics:

• It is less expensive (i.e. it is cheaper) They cost less per byte.
• It is slow (the access time of storage devices are measured in milliseconds i.e thousands of a second). It has low speed.
• It is not part of the CPU
• It has a higher/larger storage capacity.
• It is used to store large quantities of data.
• It is non-volatile (its contents are retained even when the power is switched off from the computer.
• It is permanent. (I.e. record storage is permanent). It is a permanent type of storage.
• It is used to store data that are not needed for immediate processing.
• It is made up of magnetic bubbles
• It is called backing storage
• It is used for mass storage needs
• It operates on the principle of magnetism.

Types of magnetic storage hardware

Two common types of magnetic storage hardware are:

l. Disks (magnetic disks) 2. Tapes (magnetic tapes)

MAGNETIC DISK STORAGE

• The circular platters on each side of the magnetic disk are about 35cm in diameter.
• The circular platters on each side of the magnetic disk are very smooth.
• The circular platters on each side of the magnetic disk are coated with a metal oxide.

Characteristics of magnetic disk units

1. Provide fast memory search
2. Have large storage capacity (iii) Use random access method to retrieve data

(iv) It is fast and to read an index

DANGERS/THREATS TO DISK (DISK ENVIRONMENTAL PROBLEMS)

The great threats/dangers to disk are: – smoke, dust, lint and fingerprints. These items can jam under the “lightning fast” read/ write heads, causing permanent damage to the smooth surface and thereby destroying data files.

Two basic types of magnetic disk media are:

• It is a type of magnetic media that stores items using magnetic patterns.
• It consists of several inflexible, circular disks called PLATTERS (or PLATES).

A platter in a disk is made of aluminium, glass or ceramic and is coated with a magnetic substance i.e. iron oxide that allows items to be magnetically recorded on its surface. Often, several platters are stacked together to create a disk park. A disk pack is easy to handle.

Example

One type of disk pack consists of I I to 14 — each-wide disks. It is about 6 inches high, weighs about 9 kilograms, and can store over 500 million characters.

A disk park is easy to handle

On hard disks, the platters (or plates), the red/write heads, and the mechanism for moving the heads across the surface of the disk are enclosed (sealed) in an airlight case/ module that protects platters from contamination.

• It is also a read/write storage media; that is you can both read from and write on a hard disk any number of times).
• It can be non removable (i.e. permanent) or removable.
• On microcomputer, hard disks are permanently mounted/housed inside the computer chassis (system unit).
• The capacity of a fixed disk in modern desktop personal computers ranges from 20 MB to 50 GB.
• On minicomputers and mainframes, hard disks can be permanent (non-removable or removable.

THE HARD DISK DRIVE – SUB- DIVISIONS OF THE HARD DISK

The hard disk is further sub-divided into two types: (a) Fixed disk or inflexible disk: It is not portable

(b) Removable disk.

FIXED DISK (FIXED HARD DISK)

• It is a type of magnetic media that stores items using magnetic patterns.
• It also a read/write storage media; (that is you can both read from and write on a hard disk any number of times)
• This is non removable magnetic disk assemblages used in magnetic disk units.
• On microcomputer, fixed disks are permanently mounted/housed inside the computer chassis (system unit)
• The capacity of a fixed disk in modern desktop personal computers ranges from 20 MB to I
• On microcomputers and mainframes, fixed disks can be permanent or removable
• It is not portable.
• It allows higher speeds greater data recording densities, and closer tolerances within a sealed, more stable environment.
• Fixed disks can be stacked together. The result is called a disk pack.

A disk pack is easy to handle.

FLEXIBLE DISK, (FLOPPY DISK), FLOPPY OR DISKETTE

OR MAGNETIC DISKETTE

It is a disk that consists of polyester film coated with an iron oxide compound.

It is a thin, circular, flexible, plastic disk with a magnetic coating enclosed in square-shaped plastic shell.

Characteristics of diskettes

1. It is portable
2. It is not expensive
3. It is square shape (iv) It is reusable

(v) It is easy to store

A floppy disk drive —is a device that can read from and write to a floppy disk.

Standard types of diskettes

There are two standard types of diskettes

1. The 5 ¹/4 inches diskettes
   • This is an old type of diskettes and it is being phased out.
   • It is in a soft (flexible) housing (jacket)
   • Its capacity ranges from 356 KB to over 1 MG of data.
2. The 3 ¹/2 inches diskettes type.
   • It is a new type and is still in use
   • It is mounted in a hard plastic cover (housing)
   • It is has a larger/ higher storage capacity
   • It weighs less
   • It consumes less power
   • It is smaller, studier and easier to store. It lifts into a T- shirt pocket or purse.

DISK CAPACITIES

USES OF DISKETTES

Diskettes are used:

1. To move data and programs from one computer to another
2. To back up critical data on the fixed disk.

THE MAIN FORCES THAT ARE HOSTILE TO THE DISKETTE (FLOPPY DISK OR FLOPPIES)

Floppies are endangered by several factors (things, or forces)

The main forces (things) that are hostile (dangerous) to floppies are

1. Dust
2. Magnetic fields
3. Liquids
4. Temperature extremes
5. Vapours

HOW TO HANDLE DISKETTES:

RULES FOR TAKING CARE OF FLOPPIES

1. Do not touch the disk surface.it is easily contaminated, which causes errors.
2. Do not use alcohol thinners or freon to clean the disk
3. Do not use magnetic or magnetized objects near the disk. Data can lost from a disk exposed to a magnetic field
4. Do not bend or fold the disk
5. Do not place heavy objects on the disk
6. Do not use rubber band or paper clips on the disk
7. Do not use erasers on the disk
8. Do not expose the disk to excessive heat or sunlight
9. Apply the index label to the right of the manufacture
10. Write on the index label with left-tip pen only

1 1 . Insert carefully by grasping upper edge

THE ARITHMETIC – LOGIC UNIT (ALU)

Is a component of the CPU (central processing unit) that performs arithmetic operations and logical operations and controls the speed of those operations. Is the calculating device for the computer.

PARTS OF THE ALU

The ALU is made up of two sections or parts:

1. THE ARITHMETIC SECTION (OR ARITHMETIC PART)

This is a part of the ALU, which deals with the arithmetic operations.

Some examples of arithmetic operations performed by the arithmetic section (or arithmetic part) of the ALU are: addition, substraction, multiplication and division.

2. THE LOGIC SECTION (OR THE LOGIC PART)

This is a part of the ALU, which handles or deals with the logical operations (or decision making operations)

Some examples of logical operations performed by the logical section (or logical part) of the ALU are: comparing, selecting, matching, sorting and merging.

FUNCTIONS OF THE ALU

The Arithmentic — logical Unit has two main functions:

1. To do (carry out) arithmetic operations e.g. addition, subtraction, multiplication and division.
2. To do (perform) logic operations e.g. comparing, selecting, matching, sorting and merging.

The ALU does not store data. It merely performs the necessary manipulations. For example; if a program tells the computer to add or subtract two or more numbers; the control unit has those numbers copied into special memory areas called registers or accumulators. The ALU then manipulates these memory areas and returns the result to the appropriate memory location as directed by the control unit.

CHARACTERISTICS OF THE ALU

1. It receives commands from the control unit (CU)
2. It contains additional storage locations called REGISTERS

The ALU does not store data. It merely perfoms the necessary manipulation

TYPES (CLASSIFICATION) OF COMPUTERS

, MICROCOMPUTERS:

Are the most widely used and the fastest growing type computers

They run easy — to — use application. There are two categories of microcomputers

• Desk-tops: – They fit on desk top, and are used by a wide range of people. Personal computers (PC) and Workstations are types of desktop computers.
• Portables: – Small and light, easy to move from one place to another.

Examples are: Laptops, Notebooks, and Sub notebooks

, MINICOMPUTERS: –

They fall between Mainframe and Microcomputer in their processing speed and data-storing capabilities. They are used for special purposes e.g. in researches or monitoring a particular manufacturing process.

• SUPERCOMPUTERS:

Are the most powered high capacity computers used by very large organizations, e.g. NASA for tracking space explorations.

, MAINFRAMES:

Are large computers occupying specially wired, air conditioned rooms. They have great processing speed and data storage. Are used by banks, government agencies insurance companies, Airline reservation systems etc.

TYPES OR CLASSIFICATION OF COMPUTERS

COMPUTERS

THE PROCESSOR OR CENTRAL PROCESSING UNIT (CPU)

Objectives

This unit is intended to enable students to understand:

• The meaning of CPU
• Parts of CPU
• Functions of the CPU
• Block diagram to Data and Command flow
• Meaning of main memory
• Major divisions of the main memory
• The RAM
• Functions of RAM
• The ROM
• Function of ROM
• Differences between RAM and ROM

THE PROCESSOR or CENTRAL PROCESSING UNIT (CPU)

THE CENTRAL PROCESSING UNIT (CPU)

A CPU is the central processing unit,Basically its the brain of computer.Also called a processor. Is the part of the computer system that runs the program instructions.

Is the part of the computer system that follows the instructions to manipulate (or change) data into information.

COMPONENTS (PARTS) OF THE CPU (PROCESSOR)

The CPU is made up (or consists) of two main parts. These are:

1. The Arithmetic — Logic unit (ALU)
2. The Control Unit (CU)

The Arithmetic Logic Unit

Main functions

(i)Performs mathematical Operations(+

(ii)Performs Logic operations(=,>,< )

Control Unit

Main functions

(i)Control all functions of computer

(ii)Control ALU

BLOCK DIAGRAM

CPU

There are FEW AUTHORS who say that the CPU is made up (or consists) of THREE main parts. These are:

1. The control unit (CU)
2. The Arithmetic- Logic Unit (AIU)
3. The main memory unit (MMU)

It should be noted here that this view is a misconception.

FUNCTIONS OF THE CPU OR PROCESSOR

The basic functions of the CPU are following: –

(i) To control the sequence of operations according to instructions (ii) To give commands to all other parts of the computer system (iii) To carry out processing (i.e. to process data into information)

4. To send processed results to the output
5. To store data and all the instructions.

OUTPUT DEVICES

These are devices that give result from a computer.

E.g.’ Printers, Plotters, Speaker, Fax- machine, Monitors, Projectors, Smart card.

TYPES OF OUT PUT DEVICES

i) SOFT COPY OUT PUT DEVICES ii) HARD COPY OUTPUT DEVICES

SOFT COPY OUT PUT DEVICES

1) MONITORS

Output devices used to display images and text.

AD VANTAGES

• Relatively cheap – Reliable
• They are quite
• Do not want paper

2) SPEAKERS

Output device which produce sound from the computer.

3) Light – Emitting diode (LED)

These are small power device which emit light.

Uses

Are used to indicate various events

E.g.:

• Power is on
• Hard disk is in operation
• Monitor is working

HARD COPY OUTPUT DEVICES

Produces hard copy out-put.

• Printers – Fax machines
• plotters
• Some photocopy machine can print

PRINTERS

Produce images or text on a paper.

TYPES OF PRINTERS

l) Impact printer

2) Non- impact printer

1. IMPACT PRINTER

Produce characters object by using hammers or pun shield on a print head

E.g; Dot- matrix printer

HOW IT WORKS

Printer head has a set of pins which hit an ink ribbon to form characters on paper.

Uses:-Used to print multiple copies black and white text.

AD VANTAGES – Low running cost – Purchase cost is low

DISADVANTAGES

• Wet the paper
• Make noise
• Low quality

-Difficult to edit

2. NON-IMPACT PRINTER

These are printers which produce characters without striking the paper. No direct contact between paper and print head.

1. Ink jet printer
2. Laser printer
3. Thermal transfer printer

INK JET PRINTER

This is the non- impact printer which uses tiny nuzzles to form the character or graphic image.

Uses

• Used commonly at home and schools
• Can be used in offices

AD VANTAGES

• Produce high quality copies – Produce colored copies
• Relative less expensive – Easy to edit.

LASER PRINTER

The toners is transferred to the paper and then fixed by heat and pressure.

Uses

– Office – School – Home

AD VANTAGES – Are quite – Are fast – Produce high quality copies – Running cost is less

BLOCK DIAGRAM FOR DATA CO.M.M.^S,.NI) FLOW IN A COMPUTER

CPC

COMPUTER MEMORY

• MEMORY (PHYSICAL MEMORY) is the actual chip that is capable to hold (store) data and programs (instructions) in use by the CPU.
• A MEMORY UNIT is the internal storage (main memory) area in a computer system.

TYPES OF MEMORY

(i)Primary memory/Main memory

(ii)Secondary memory/Backup memory

MAIN MEMORY

1. Is a small electronic part of the CPU (or computer) which stores all data and instructions (programs) before they can be used in processing (i.e between the processing steps, and after processing is completed but before output).
2. Is the memory that holds (stores) all data and instructions (programs) that will be needed shortly by the CPU.
3. Is a microelectronic semiconductor storage circuitry.

CLASSIFICATION OF THE MAIN MEMORY

THE MAIN MEMORY of the computer can be classified into two main memory sections.

1. The Random Access Memory (RAM)
2. The Read — Only memory (ROM) CHARACTERISTICS OF RAM

It is limited in size (ii) It is expensive

3. It is fast
4. It is used to hold data and programs that are actively being processed.
5. It contains application programs developed by computer users in order to solve specific problems.
6. It is designed to serve the computer user.

FUNCTIONS (USES OR TASKS) OF RAM

The main functions of RAM are:

It holds (stores) data for processing.

2. It holds (stores) instructions (application programs) for processing data
3. It holds (stores) processed data (that is information) waiting to be sent to an output device or secondary storage device.

FUNCTIONS (USES OR TASKS) OF ROM

The main functions of ROM are:

1. To store the data and instructions (programes) that the necessary for the normal functioning of the computer system hardware (i.e. it stores operating system data and instructions)
2. To store control programs that are necessary for the initial activation of the hardware when power is switched on.

CHARACTERISTICS OF ROM

It is used to hold initialization instructions for the computer to start itself and for certain other repetitive, specialized functions.

2. It contains control programs built-in or installed by the manufacturer of the computer system at the factory.
3. It is designed to serve the hardware of the computer system.
4. Contents of ROM are inserted (built in) at the factory by the manufacture; buyers have little to do with it.
5. The contents of Rom cannot be changed
6. It is permanent

USES OF THE MAIN MEMORY

Some uses of the main memory are: (i) To store instructions waiting to be obeyed

(ii) To store instructions being obeyed (iii) To store awaiting processing

4. To store data currently being processed
5. To store data waiting output.

DISADVANTAGES OF THE MAIN MEMORY

The main memory has the following disadvantages:

1. It is limited. There is a capacity beyond which it cannot be extended.
2. It is expensive. The technology involved and the elements used in making them are expensive
3. It is volatile. (i.e. it loses its contents immediately when power is switched off)

DIFFERENCES BETWEEN RAM AND ROM

		ROMAD -ONLY ME-MOR\		RAMNDONI -ACCESS MEMOR\
	1.11.111. v.	Its contents can only be read.Nothing can be written on to it.It is non —volatile (i.e. the contents of the ROM are not lost when power IS cut oft)The amount of ROM in a computer is usually small. It makes about 30% ofthe mam memory.The contents of ROM are Inserted(built in) at the factory by the manufacturer; buyers have little to do with it.The contents of ROM cannot bechanged.It is permanent.It is used to hold mitialization mstftlctions for the computer to staff itself and for certain other repetitivespecialized ftnctions.It contams control programs built-m or Installed by the manufacturer of the computer system at the factory. It is designed to serve the hardware of the computer system.	1.11.111.v.VIM.	It is possible to read and write. It is volatile (its contents are lost when power is cut off). It requtres a steady flow of electricity to mamtam its contents.The amount of RAM m a computer vanes from computer to computer.However, it make about 70% ofthe mam memory.Its contents are developed by computer users In order to solve specific problems.The components of RAM can be changed.It is temporary It is limited m Size It is expensiveIt is fast.It is used to hold data andprograms that are actively bemg processed.It contams application programs developed by the computer users 111 order to solve specific problems.It is designed to serve the computer users.

SECONDARY MEMORY

This is the memory which found inside and outside computer system unit.

E.g: Hard disk, DVD (Digital Versatile Disk), VCD (Video Compact Disk) CD (Compact Disk) Flash Disk, Memory card etc.

NOTE: CD are inserted into a CD ROM (COMPACT DISK READ ONLY MEMORY)

DVD (DIGITAL VERSATILE DISK)

A number of slightly difference technologies make recordable DVDs available. These include.

• DVD —ROM : Read only memory which is typically stamped in a DVD press , not burnt, and can only be read from Any mass produces DVD title is on a DVD —ROM disk.
• DVD -+ Recordable, which can usually be written to once in a long, continuous write in a DVD burner.
• DVD -+ RW: Re- writable which is disk that is rate to be burned up to 100 times.
• DVD — RAM : Rand Access Memory , which can be used almost like a portable hard disk, with any one spot on the disk surface rated to be written to up to 1000,000 times.

DIFFERENT BETWEEN PRIMARY AND SECONDARY MEMORY

VGA (Video Graphics Array)

(Video Graphics Array) Is widely used analyzing interface between a computer and monitor that uses a 15 —pin plug and socket Order CRTS used VGA and flat LCD panels typically have both analog and digital DVI. However, newer PCs may have only DVI or display.

SOUND CARD

A sound card (also known as an audio card) is an internal card that facilitates the input and output programs.

GRAPHIC CARD

Is an expansion card where function is to generate output images.

COMPUTER STORAGE

A computer system has two main types of storage/storage areas: –

1. Main storage (also called primary memory, internal memory
2. Secondary storage(also called auxiliary storage, backing storage

	ILS.LNMEMORY		MEMORY
	Itis expensive. (Thisisbecauseitisusually made up of materials such as magletic cores, semiconductor, circuits, or magletic bubble that are hi#y expensive). They cost less per byte.		Itisless expensiveThey cost less perbyte.
	It is fast (the access tmle of memory devices is measured In nanoseconds i.e. billionths ofa second). Ithashigh sped		It is slow (the access tmle of storage devices of measured In milliseconds i.e. thousandth ofa second)ithas low sped
	It is part ofthe CPU		It is not part of CPU
		Itistemporary.(l.e. there isno permanent record storage) it is a temporary type of storage		It is permanent (i.e. record storage is pennanett).Itispenna1E1ttype ofstorage.
		It is used to store data and instructions which are needed betweenprocessmgsteps and supplies them to the control Imit and ALU during processing.		Itisusedto store data that are not needed for immediate processing.
		It is made of microelectronic semiconducctor storage circuitry (i.e. semiconO:tor memory’ chips on the circuit boards in the main systema Init.		It is made up of magnetic bubbles.
		It is called the working memory of the computer		It is called backing storage
		It is used for immediate access requirements		It is used for mass storage needs

SECONDARY STORAGE DEVICES AND SECONDARY STORAGE MEDIA

A STORAGE MEDIUM — is a physical material on which items (data, Instructions and information) are kept e.g. disk

A STORAGE DEVICE is the mechanism used to record and retrieve items to and from a storage medium.

Examples of secondary storage devices/ secondary storage media

• Floppy disk (diskette), magnetic diskette.
• Magnetic disk or hard disk
• Magnetic tape
• Optical disks e.g. CD,CD-ROM WORM and DVD, DVD-ROM, DVD-RAM and rewritable optical disks (cailed floptical, magneto-optic)

Types of storage and seconþary storage devices.

Computer storž:e

CHARACTERISTICS OF SECONDARY STORAGE DEVICES

Secondary storage devices have a several common characteristics:

• It is less expensive (i.e. it is cheaper) They cost less per byte.
• It is slow (the access time of storage devices are measured in milliseconds i.e thousands of a second). It has low speed.
• It is not part of the CPU
• It has a higher/larger storage capacity.
• It is used to store large quantities of data.
• It is nonvolatile (its contents are retained even when the power is switched off from the computer.
• It is permanent. (I.e. record storage is permanent). It is a permanent type of storage.
• It is used to store data that are not needed for immediate processing.
• It is made up of magnetic bubbles
• It is called backing storage
• It is used for mass storage needs
• It is operates on the principle of magnetism.

Secondary storage devices operate on the principal of magnetism.

Types of magnetic storage hardware

Two common types of magnetic storage hardware are:

l. Disks (magnetic disks) 2. Tapes (magnetic tapes)

MAGNETIC DISK STORAGE

• The circular platters on each side of the magnetic disk are about 35cm in diameter.
• The circular platters on each side of the magnetic disk are very smooth.
• The circular platters on each side of the magnetic disk are coated with a metal oxide.

Characteristics of magnetic disk units

1. Provide fast memory search
2. Have large storage capacity (iii) Use random access method to retrieve data

(iv) It is fast and to read an index

DANGERS/THREATS TO DISK (DISK ENVIRONMENTAL PROBLEMS)

The great threats/dangers to disk are: – smoke, dust, lint and fingerprints. These items can jam under the “lightning fast” read/ write heads, causing permanent damage to the smooth surface and thereby destroying data files.

Two basic types of magnetic disk media are:

• It is a type of magnetic media that stores items using magnetic patterns.
• It consists of several inflexible, circular disks called PLATTERS (or PLATES).

A platter in a disk is made of aluminium, glass or ceramic and is coated with a magnetic substance i.e. iron oxide that allows items to be magnetically recorded on its surface. Often, several platters are stacked together to create a disk park. A disk pack is easy to handle.

Example

One type of disk pack consists of I I to 14 — each-wide disks. It is about 6 inches high, weighs about 9 kilograms, and can store over 500 million characters.

A disk park is easy to handle

On hard disks, the platters (or plates), the red/write heads, and the mechanism for moving the heads across the surface of the disk are enclosed (sealed) in an airlight case/ module that protects platters from contamination.

• It is also a read/write storage media; that is you can both read from and write on a hard disk any number of times).
• It can be non removable (i.e. permanent) or removable.
• On microcomputer, hard disks are permanently mounted/housed inside the computer chassis (system unit).
• The capacity of a fixed disk in modern desktop personal computers ranges from 20 MB to 50 GB.
• On minicomputers and mainframes, hard disks can be permanent (non-removable or removable.

THE HARD DISK DRIVE – SUB- DIVISIONS OF THE HARD DISK

The hard disk is further sub-divided into two types: (a) Fixed disk or inflexible disk: It is not portable

(b) Removable disk.

FIXED DISK (FIXED HARD DISK)

• It is a type of magnetic media that stores items using magnetic patterns.
• It also a read/write storage media; that is you can both read from and write on a hard disk any number of times)
• This is non removable magnetic disk assemblages used in magnetic disk units.
• On microcomputer, fixed disks are permanently mounted/housed inside the computer chassis (system unit)
• The capacity of a fixed disk in modern desktop personal computers ranges from 20 MB to I
• On microcomputers and mainframes, fixed disks can be permanent or removable
• It is not portable.
• It allows higher speeds greater data recording densities, and closer tolerances within a sealed, more stable environment.
• Fixed disks can be stacked together. The result is called a disk pack.

A disk pal is easy to handle.

FLEXIBLE DISK, (FLOPPY DISK), FLOPPY OR DISKETTE

OR MAGNETIC DISKETTE

• It is a disk that consists of polyester film coated with an iron oxide compound.
• It is a thin, circular, flexible, plastic disk with a magnetic coating enclosed in square-shaped plastic shell.

Characteristics of diskettes

1. It is portable
2. It is not expensive
3. It is square shape (iv) It is reusable

(v) It is easy to store

A floppy disk drive —is a device that can read from and write to a floppy disk.

Standard types of diskettes

There are two standard types of diskettes

1. The 5 ¹/4 inches diskettes
   • This is an old type of diskettes and it is being phased out.
   • It is in a soft (flexible) housing (jacket)
   • Its capacity ranges from 356 KB to over 1 MG of data.
2. The 3 ¹/2 inches diskettes type.
   • It is a new type and is still in use
   • It is mounted in a hard plastic cover (housing)
   • It is has a larger/ higher storage capacity
   • It weighs less
   • It consumes less power
   • It is smaller, studier and easier to store. It lifts into a T- shirt pocket or purse.

DISK CAPACITIES

USES OF DISKETTES

Diskettes are used:

1. To move data and programs from one computer to another
2. To back up critical data on the fixed disk.

THE MAIN FORCES THAT ARE HOSTILE TO THE DISKETTE (FLOPPY DISK OR FLOPPIES

Floppies are endangered by several factors (things, or forces)

The main forces (things) that are hostile (dangerous) to floppies are

1. Dust
2. Magnetic fields
3. Liquid (iv) Temperature extremes

(v) Vapors

HOW TO HANDLE DISKETTES:

RULES FOR TAKING CARE OF FLOPPIES

1. Do not touch the disk surface.it is easily contaminated, which causes errors.
2. Do not use alcohol thinners or freon to clean the disk
3. Do not use magnetic or magnetized objects near the disk. Data can lost from a disk exposed to a magnetic field
4. Do not bend or fold the disk
5. Do not place heavy objects on the disk
6. Do not use rubber band or paper clips on the disk
7. Do not use erasers on the disk
8. Do not expose the disk to excessive heat or sunlight
9. Apply the index label to the right of the manufacture
10. Write on the index label with left-tip pen only

1 1 . Insert carefully by grasping upper edge

THE ARITHMETIC – LOGIC UNIT (ALU)

Is a component of the CPU (central processing unit) that performs arithmetic operations and logical operations and controls the speed of those operations. Is the calculating device for the computer.

PARTS OF THE ALU

The ALU is made up of two sections or parts:

1. THE ARITHMETIC SECTION (OR ARITHMETIC PART)

This is a part of the ALU, which deals with the arithmetic operations.

Some examples of arithmetic operations performed by the arithmetic section (or arithmetic part) of the ALU are: addition, subtraction, multiplication and division.

2. THE LOGIC SECTION (OR THE LOGIC PART)

This is a part of the ALU, which handles or deals with the logical operations (or decision making operations)

Some examples of logical operations performed by the logical section (or logical part) of the ALU are: comparing, selecting, matching, sorting and merging.

FUNCTIONS OF THE ALU

The Arithmetic — logical Unit has two main functions:

1. To do (carry out) arithmetic operations e.g. addition, subtraction, multiplication and division.
2. To do (perform) logic operations e.g. comparing, selecting, matching, sorting and merging.

The ALU does not store data. It merely performs the necessary manipulations. For example; if a program tells the computer to add or subtract two or more numbers; the control unit has those numbers copied into special memory areas called registers or accumulators. The ALU then manipulates these memory areas and returns the result to the appropriate memory location as directed by the control unit.

CHARACTERISTICS OF THE ALU

1. It receives commands from the control unit (CU)
2. It contains additional storage locations called REGISTERS

The ALU does not store data. It merely performs the necessary manipulation