4.1 Description Of Hardware
A desktop computer before is really a system of many parts working together. The physical parts, which you can see and touch, are collectively called hardware.
The figure below shows the most common hardware in a desktop computer system. Your system may look a little different, but it probably has most of these parts. A laptop computer has similar parts but combines them into a single notebook-sized package.
Figure 4a: The Computer System
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The computer system components parts were described in chapter 2 of this book and almost all the components described are parts of computer hardware. In this chapter the computer hardware will be describe based on the computer hardware configuration which include both the directly visible and invisible hardware. This hardware configuration is as given in figure 4b below.
Figure 4b. Computer Hardware Configuration
Note: Computer Hardware can be divided basically into two; the CPU and Peripherals. CPU is made up of control unit, Arithmetic
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and logic unit and Main memory. While the peripheral is made up of Input devices, Output devices and Backing storage.
The components of computer hardware based on the diagram in figure 4b are the CPU and Peripherals (input and output units). Some of the peripherals were described in chapter two of this book.
4.2 Central Processing Unit
This is an integral part of system unit of computer system that made up of other components like; the main storage, the control unit and the arithmetic/logic unit.
Main Storage
The Main Storage contains two types of memory chips, named the Random-Access Memory (RAM) and Read-Only Memory (ROM). RAM is a memory that has the same access time for all locations. It is used to store data and program temporarily whenever they are needed in main memory. It is constantly being re-used for different data items or programs as required. Static RAM holds its memory so long as there is a power supply. Dynamic Ram (DRAM) has to be refreshed by reading and rewriting the contents very frequently. RAM is volatile, that is, the con-tents of RAM are lost when the power supply is switched off. ROM (integrated circuit) is used to store vital data and programs which need to be held within the main memory at all times. The contents of ROM are permanently set during the manufacture of the computer.
However, there are other ways of putting programs and data into ROM. Programmable Read-Only Memory (PROM) is a type of ROM that is manufactured as an empty storage array and is later permanently programmed by the user. Erasable PROM (EPROM) is a type of PROM whose data can be erased by a special process so new data can be written as if it were a new PROM. Arithmetic/Logic Unit (ALU)
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The Arithmetic/Logic Unit (ALU) consists of adder/subtractor, electronic circuit and working registers to which operands may be transferred during an operation. The ALU performs the
- Arithmetic Operations
- Data Handling Operations
- Logical Functions.
The data to be processed are taken from main storage, stored in the working registers, processed and the results placed back in the main storage.
Control Unit
The Control Unit examines the individual instructions in the users‘ program one by one, interprets each instruction and causes the various circuits to be activated to perform the functions specified. Some of the functions of the control unit are:
- It co-ordinates the various parts of the computer system to form a composite integrated data processing system.
- It controls the transfer of data between and within the working stores as required by the program.
- It controls input/output. Once the program controller has initiated a read/write operation, the control unit continues to monitor the operation to ensure that it is satisfactorily completed.
- In time-sharing or on-line systems, the control unit co- ordinates the several concurrent peripheral operations while data is processed internally within the CPU.
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4.3 Peripherals Input & Output Devices
4.3.1 Input Device
Computer Input is the process of transferring data from computer- sensible media into the main storage of the computer. The equipment which converts data been captured on a source documents into machine sensible form is called an input device. The following terms are related to inputting data into computer.
- Data Capture is the term used to describe the process of collecting data in machine sensible form at its source.
- Data Collection is the term used to describe the process of recording the data on source document and subsequently converting it into machine sensible form for input to the computer.
- Data Conversion is the process of transforming the data on source documents into machine sensible form before carrying out the input operation.
Type of Input Device
- Direct Input Devices allow data to be input into the computer without any need for data conversion. Examples are: keyboard terminals, mouse, trackballs, scanners, joystick, bar-code readers, touch screens, OCR, OMR and MICR equipment.
- Indirect Input Devices accept data from source documents and convert it into computer-sensible form for subsequent input into the computer. Examples are: magnetic tape, magnetic disk, compact disk and diskette drives.
Input devices can also be classified as manual or automated. Manual input devices include keyboard, mouse, trackball, joystick, bar-code readers, scanners, and touch screens. Automated input
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devices include MICR, OCR, OMR, magnetic stripe and smart cards.
Computer keyboard
A keyboard is used mainly for typing text into your computer. Like the keyboard on a typewriter, it has keys for letters and numbers, but it also has special keys like:
- The function keys, found on the top row, perform different functions depending on where they are used.
- The numeric keypad, located on the right side of most keyboards, allows you to enter numbers quickly.
- The navigation keys, such as the arrow keys, allow you to move your position within a document or webpage.
Some modern keyboards come with “hot keys” or buttons that give you quick and one-press access to programs, files, or commands. Other models have volume controls, scroll wheels, zoom wheels, and other gadgets. For details about these features, check the information that came with your keyboard or computer, or go to the manufacturer’s website.
Figure 4c. Modern computer keyboard
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Three odd keys
So far, we’ve discussed almost every key you’re likely to use. But for the truly inquisitive, let’s explore the three most mysterious keys on the keyboard: PRINT SCREEN, SCROLL LOCK, and PAUSE/BREAK.
Print Screen (or PRT SCN)
A long time ago, this key actually did what it says—it sent the current screen of text to your printer. Nowadays, pressing PRINT SCREEN captures an image of your entire screen (a “screen shot”) and copies it to the Clipboard in your computer’s memory. From there you can paste it (CTRL+V) into Microsoft Paint or another program and, if you want, print it from that program. More obscure is SYS RQ, which shares the key with PRINT SCREEN on some keyboards. Historically, SYS RQ was designed to be a “system request,” but this command is not enabled in Windows.
Scroll Lock (or SCR LK)
In most programs, pressing SCROLL LOCK has no effect. In a few programs, pressing SCROLL LOCK changes the behavior of the arrow keys and the PAGE UP and PAGE DOWN keys; pressing these keys causes the document to scroll without changing the position of the cursor or selection. Your keyboard might have a light indicating whether SCROLL LOCK is on.
Pause/Break
This key is rarely used. In some older programs, pressing this key pauses the program or, in combination with CTRL, stops it from running.
Electronic Mouse
A mouse is a small device used to point to and select items on your computer screen. Although mice come in many shapes, the typical
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mouse does look a bit like an actual mouse. It’s small, oblong, and connected to the system unit by a long wire that resembles a tail.
Some newer mice are wireless. When you move the mouse with your hand, a pointer on your screen moves in the same direction. (The pointer’s appearance might change depending on where it’s positioned on your screen.) When you want to select an item, you point to the item and then click (press and release) the primary button. Pointing and clicking with your mouse is the main way to interact with your computer.
A mouse typically has two buttons: a primary button (usually the left button) and a secondary button (usually the right button). The primary button is the one you will use most often. Most mice also include a scroll wheel between the buttons to help you scroll through documents and webpages more easily. On some mice, the scroll wheel can be pressed to act as a third button. Advanced mice might have additional buttons that can perform other functions.
Figure 4d. Parts of a mouse
Holding and Moving the Mouse
Place your mouse beside your keyboard on a clean, smooth surface, such as a mouse pad. Hold the mouse gently with your index finger resting on the primary button and your thumb resting on the side. To move the mouse, slide it slowly in any direction. Don’t twist it; keep
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the front of the mouse aimed away from you. As you move the mouse, a pointer on your screen moves in the same direction. If you run out of room to move your mouse on your desk or mouse pad, just pick up the mouse and bring it back closer to you. Hold the mouse lightly, keeping your wrist straight. Figure 4d illustrate the explanation given.
Figure 4d. Mouse holding technique
Pointing, clicking, and dragging: Pointing to an item on the screen means moving your mouse so the pointer appears to be touching the item. When you point to something, a small box often appears that describes the item. For example, when you point to the Recycle Bin on the desktop, a box appears with this information: “Contains the files and folders that you have deleted.”
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Figure 4e.Pointing to an object to reveals a descriptive message about it
The pointer can change depending on what you’re pointing to. For example, when you point to a link in your web browser, the pointer changes from an arrow to a hand with a pointing finger . Most mouse actions combine pointing with pressing one of the mouse buttons. There are four basic ways to use your mouse buttons: clicking, double-clicking, right-clicking, and dragging.
- Clicking (single-clicking): To click an item, point to the item on the screen, and then press and release the primary button (usually the left button). Clicking is most often used to select (mark) an item or open a menu. This is sometimes called single-clicking or left-clicking.
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- Double-clicking: To double-click an item, point to the item on the screen, and then click twice quickly. If the two clicks are spaced too far apart, they might be interpreted as two individual clicks rather than as one double-click.
- Double-clicking is most often used to open items on your desktop. For example, you can start a program or open a folder by double-clicking its icon on the desktop.
- Right-clicking: To right-click an item, point to the item on the screen, and then press and release the secondary button (usually the right button). Right-clicking an item usually displays a list of things you can do with the item. For example, when you right-click the Recycle Bin on your desktop, Windows displays a menu allowing you to open it, empty it, delete it, or see its properties. If you’re ever unsure of what to do with something, right-click it. Right-clicking the Recycle Bin opens a menu of related commands
Figure 4f. Right clicking recycle bin
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- Dragging: You can move items around your screen by dragging them. To drag an object, point to the object on the screen, press and hold the primary button, move the object to a new location, and then release the primary button. Dragging (sometimes called dragging and dropping) is most often used to move files and folders to a different location and to move windows and icons around on your screen.
Using the Scroll Wheel
If your mouse has a scroll wheel, you can use it to scroll through documents and webpages. To scroll down, roll the wheel backward (toward you). To scroll up, roll the wheel forward (away from you).
Customizing Your Mouse
You can change your mouse settings to suit your personal preferences. For example, you can change how fast your mouse pointer moves around the screen, or change the pointer’s appearance. If you’re left-handed, you can switch the primary button to be the right button.
Trackballs
A trackball is like a mouse turned upside down. It is a stationary device related to the mouse. It has a roller ball with only its top exposed outside its case. The cursor on the screen is moved whenever the roller ball is turned. Pressing buttons on the trackball activates various activities represented by the icon selected.
(a) A mouse
(b) A trackball
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Touch Screens
Touch screen is a special screen that is able to detect the position on the screen that a user‘s finger is touching or pointing at. A standard computer screen is covered by two very thin pieces of plastic. Embedded into the plastic is a fine wire and that is linked to the computer. When someone touches the grid, the computer can deduce exactly where the touch is made.
Joysticks
Joysticks are used more on video games than with PCs. A joystick has a short vertical handle that can be tilted forwards and backwards, left and right. A joystick allows the user to point to objects on the screen in the same way as a mouse, but it is more convenient for following a moving target. It may have one or more buttons on it.
Light Pen
A light pen allows the user to point the pen at different parts of a screen to select an option or draw a graphic, so it is like very accurate Touch screens. The use of light pens is quite rare.
Optical Scanners
Optical scanning devices read text or graphics and convert them into digital input for the computer. Thus, optical scanning enables the direct entry of data from source documents into a computer system. Optical scanners employ photoelectric devices to scan the characters being read. Reflected light patterns of the data are converted into electronic impulses that are then accepted as input into the computer system. Optical Character Recognition (OCR) is a form of optical scanning.
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Voice Recognition
Voice recognition systems analyse and classify speech or vocal tract patterns and convert them into digital codes for entry into a computer system. Voice recognition systems with large vocabularies require training the computer to recognise your voice in order to achieve a high degree of accuracy
Magnetic Stripe
Swipe and credit cards have black iron oxide coating of magnetic stripe on the reverse side, and it is this that the computer recognises. The black stripe holds information, such as customer account numbers, that can be accessed only by a special magnetic reading device. The reading device converts the information into computer usable form, for example, at the automated teller machines found at banks and at credit card authorization terminals.
Smart Cards
Smart Cards embed a microprocessor chip and several kilobytes of memory into debit, credit, and other cards. Smart debit cards enable the user to store a cash balance on the card and electronically transfer some of it to others to pay for small items and services. The balance on the card can be replenished in automated teller machines (ATMs) or other terminals. Smart cards are widely used to make payments in parking meters, vending machines, pay telephones, and retail stores.
Digital Cameras
Digital still cameras and digital video cameras (digital camcorders) enable the user to shoot, store, and download still photos or full motion video with audio into a PC. Then image-editing software can be used to edit and enhance the digitised images and include them in newsletters, reports, multimedia presentations, and web pages.
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Optical Character Readers
Optical character readers (OCR) are machines capable of reading printed documents directly into the computer by recognising the shape of the different characters. Reading of documents prepared in optical characters is accomplished by the use of a scanning device that reflects light from the character on to a lens where it is focused on a photoelectric cell. The cell produces a variable electric current that is unique for each character read. This process is termed optical character recognition.
Optical Mark Readers
Optical mark readers (OMR) are machines that use an artificial light source to scan marks made on OMR documents in order to determine their values. Marking is done in small horizontal shape on documents with black media such as a soft pencil. On OMR documents, predetermined positions are given certain values. The optical reader converts the mark in a position to the appropriate value. This is termed optical mark recognition (OMR).
Magnetic Ink Character Readers
Magnetic ink character readers (MICR) are machines capable of reading magnetic ink characters on MICR documents and passing the data into a computer. A MICR document has human-readable characters printed in the normal way with the use of a specially designed font but using a ferrous-based ink that is capable of magnetization.
Magnetic Ink Character Recognition (MICR) technology is employed by the computer systems of the banking industry to read cheques magnetically.
On-Line Input
This entails data being transmitted directly to the computer by the use of terminals sited at a distance from the computer and linked to
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it by communication arrangements. The computers‘ response is transmitted back to the terminal.
Bar Coding
Bar coding is the representation of code numbers or other data by bars or lines printed or embossed on a data carrier. The data carrier may be a tag, ticket, label, plastic card or a packet/can holding goods.
Universal Product Code
The Universal Product Code (UPC) system was introduced by the USA to cover the complete range of grocery products. Each product is given a unique 10-digit code that is represented in bar code form on every packet or other type of container or on labels. The bars are in pairs, each of which represents a digit according to their spacing and thickness. Certain symbols are also represented including those to indicate the start and finish of the bar coding. The European equivalent of UPC is the European Article Number (EAN).
Bar Code Readers
A bar code reader functions as follows: The bar code is scanned by a laser, which measures the thickness of the lines and the distance between them to decipher the code. Once read, the information can be transmitted to a computer. These hardware devices are often used for point-of-sale input systems in supermarkets and other outlets.
Output Devices
Computer output is the process of transferring data and information from the main storage of the computer onto a human-sensible medium or a machine-sensible medium. The principal methods of producing computer output are:
- Displayed output on a VDU screen
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- Printed output on paper
- Computer-sensible output on a magnetic medium
- Computer output on microform
- Plotters
- Sound output
Video Output
Video monitors use cathode ray tubes (CRT) technology similar to the picture tubes used in home TV sets. The clarity of the video display depends on the type of video monitor and the graphic circuit board installed in the computer. The information displayed on the screen is often referred to as soft copy. Monitors can be monochrome or colour. Monochrome monitors give a display of varying intensity on a single colour, for example, white on black background or orange/green on dark background. Colour monitors give a display with a range of colours determined by the colour circuitry in the monitor and the computer.
Printers/ Plotters
A printer is a mechanical device used for producing human-readable information on paper. A printer is connected to a computer for the sole purpose of transferring the information from the computer to paper or other media. The version printed out on paper is often referred to as hard copy. The three main categories of computer printers are line printers, serial/character printers and laser printers. A plotter contains a pen that draws lines on paper. Plotters are devices used for producing hard copies of complex graphics outputs in the form of graphs, charts, histograms and diagrams. These devices are much better than ordinary printers at handling diagrams. The technique has a wide range of use in fields such as scientific research, engineering and management information systems. They are commonly used for such tasks as producing technical drawings and road/rail networks.
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Magnetically Encoded Output
Computer output, in coded form, are written onto a magnetic medium usually for the purpose of storing updated records. The magnetic media used for the purpose include diskette, compact disk, magnetic tape, and magnetic disks.
Sound Output
A sound output device reproduces previously recorded and stored sounds. Sound output devices are the output equivalent of sound input devices. Sound output devices simply convey pre-recorded information in audio form. Speech synthesis is the production of sounds resembling human speech by electronic methods. A speech synthesis output device creates speech output from text. Speech synthesis output devices are the flipside of automatic speech recognition input devices. Speech synthesis devices convey information in audio form.
Backing Storage
Backing storage is an extension to a computer‘s internal storage. It is used for the off-line mass storage of programs, data and files that are not currently being used for processing. The types of common backing storage in use are magnetic tape, magnetic disk, compact disk, USB flash drive and floppy disk.
Magnetic Tapes
The magnetic tape consists of a strip of plastic tape coated with a magnetic material deposited in grains, each of which may be magnetized in one of two directions. A tape is held on a reel. A tape drive is used for writing data onto magnetic tape from the processor and for reading data from magnetic tape into the processor. The reading/writing operations are accomplished by a pair of read/write heads.
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Advantages of Magnetic Tape
- It is relatively inexpensive, compared to the magnetic disk.
- It has a large data storage capacity.
- It is capable of transferring data to and from the main storage of the computer at very high speed.
- Transaction data can be recorded directly onto the magnetic tape by means of magnetic tape encoding machines.
- Old data may be erased and the tape used repeatedly.
Disadvantages Of Magnetic Tape
- It is only possible to access records serially.
- Data can be accidentally erased or overwritten.
- It is not possible to read the records on tape visually.
- Updated information cannot be written back to the same location on the same tape.
- Input data must be sorted into the sequence of the master file before updating can start.
- Stringent environment control is necessary in order to eliminate dust and static electricity in the atmosphere.
Magnetic Disks
A magnetic disk or hard disk is a flat circular device, which is similar to a long-playing phonograph record. It is made of metal and each of the recording surfaces is coated with a thin layer of magnetisable iron oxide. Usually, six disks are held on a common axis, one above the other, to form a disk pack. A disk pack is mounted on a disk drive mechanism. The disk drive is used for writing data onto magnetic disk from the processor and reading data from magnetic disk into the processor. The reading/writing operations are accomplished by using a pair of read/write heads placed next to each recording surface.
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Advantages of Magnetic Disk
- A pack of disks has very high storage capacity.
- Data on tracks may be overwritten with new data.
- Disks are ideal for storing subroutines, tables and rates.
- Disks may be used for real-time remote enquiry systems.
- The speed of data transfer from the processor and to the processor is very high.
- Data can be input onto a disk without the need for sorting.
- Any item of data can be directly addressed, depending upon the method of the file organisation used.
Disadvantages of Magnetic Disk
- Disk storage devices are more expensive than many other storage media.
- Data may be accidentally erased or overwritten.
- It is more complex to program disk operations than for magnetic tape.
- Disk operations involve the locating of overflow records.
USB Flash Drive
A USB flash drive is a data storage device that includes flash memory with an integrated Universal Serial Bus (USB) interface. USB flash drives are typically removable and rewritable, and physically much smaller than an optical disc. Most weigh less than 30 grams (1.1 oz). As of January 2013, drives of up to 512 gigabytes (GB) were available. A one-terabyte (TB) drive was unveiled at the 2013 Consumer Electronics Show and became available later that year. USB flash drives are often used for the same purposes for which floppy disks or CDs were used, i.e., for storage, back-up and transfer of computer files.
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Advantages of USB Flash Drive
They are smaller, faster, have thousands of times more capacity, and are more durable and reliable because they have no moving parts
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