Hardware Fundamentals
© Copyright Brian Brown, 1992-2000. All rights reserved.

Computer Systems
A computer system is made up of a number of different sub-component systems which together allow the system to perform calculations and complicated tasks. A computer system could run payrolls, control an engine in a car, fly an airplane or allow a user to play games and balance their chequebook.

Computer systems do vary, in size, cost and power, depending upon the task that they are required to perform. In this course, we are primarily concerned about personal computer systems, suitable for small business or home use. The diagram below shows a typical personal computer system.

Fig 1: Basic Computer System

• Base Unit
  The base unit holds the computers motherboard, on which the computers memory storage area (commonly referred to as RAM) and CPU (Central Processing Unit) are located. RAM holds both programs and data, the larger the RAM size, the more complicated the programs that can be run, and the more data that can be processed. RAM is measured in Megabytes (one MB = 1 million characters). Typical sizes for today's personal computer systems is 16MB.
  
  

  The floppy drive and hard drive are storage devices that are used to keep permanent copies of programs or data. The floppy drive supports a removable media disk, which the user can take away and use on another computer system. The hard drive is considered a non-removable media disk because it is permanently fixed inside the base unit. Floppy drives support up to about 1.44MB of data, while fixed disks support 1.2GB upwards (1200MB or 1200 Million characters).

  The CPU is the device that actually runs all the programs and processes the data. Its like the motor of the car, it does all the work and makes things happen. The PSU (Power Supply Unit) is also located in the base unit, and provides power to the memory, CPU and other devices.
  

• Keyboard
  Keyboards allow users to enter commands and data into the computer system.
  
  

  An example of a command might be to run a chequebook program or dial up a remote computer. You can learn more about keyboards here.

  
  

• Monitor
  Monitors are devices that allow the computer to display information back to the user. This might be in either a text or graphical display. Monitors come in various sizes, 14", 15", 17" and so on. The larger the monitor, the more expensive it is, and the larger the image displayed on the screen is.
  
  

  Monitors have a number of important features, screen resolution refers to the number of dots in the X and Y co-ordinates (640 by 480, or 800 x 600), and refresh rate, which specifies the number of times per second that the image is drawn on the screen (60Hz means 60 times per second). You can learn more about monitors here.

  Higher screen resolutions like 1024x768 require a large monitor size like 21" (otherwise it looks so small when viewed on a 14" monitor), and also require a higher refresh rate like 72Hz, in order to prevent the image on the screen flickering.
  
  

• Mouse
  A mouse is an inverted trackball device that has a number of selection buttons associated with it. The hand moves it across a flat surface, and its position is displayed on the screen. As the mouse is moved across the surface, its position displayed on the screen is updated to reflect its movement. The buttons are used to select items and make choices on the screen.
  
  

  The mouse can significantly reduce user input by moving away from typing commands at the keyboard to clicking on buttons or other items displayed on the screen. You can learn more about the mouse here.

  
  

• Printer
  A printer allows the user to print out on paper a copy of the screen or the data that is being processed by the computer.
  
  

  Printers are available in both color and black and white. Color printers are slower and more expensive than black and white printers. In addition, the technology used to print the information on the paper varies upon the type of printer. You can learn more about printers here, and learn about the maintenance of printers here.

  
  

• Modem
  A modem is a device which allows the user to connect their computer system to another computer system. A modem attaches to a telephone line, and dials up another computer via the telephone.
  
  

  The modem converts the computer signals so that they work over the telephone circuits used by the telephone companies. A modem can be an internal device that is located inside the base unit, or, as shown here, an external device that attaches to the base unit via a cable.

  
  

Computer Keyboards and Data Processing
Computers used in data processing applications run dedicated application programs. The objective of this section is to

• outline areas of computer use in data processing
• describe the usage of computer keys in data processing

At the end of this section you should be able to

• list a number of data processing areas
• state the purpose of specific keyboard keys used for data processing

Data Processing Areas
Examples of data processing areas are

• stock control
• inventory
• ordering
• accounting
• manufacturing
• atm
• banking

It is common to find general-purpose computers (like IBM Compatible computers) used in these areas. A keyboard template is fitted over the keyboard that defines the purpose or special function performed by the keys (interpreted by the application program).

Often, other peripheral devices like bar-code wands, magnetic card swipes, and touch screens are also used as input devices.

Fig 2: Magnetic card swipe reader	Fig 3: Bar-Code wand and reader unit.

Keyboard Usage in Data Application Systems
Common keys, and their usage in data applications, are

• SHIFT used to generate other key combinations
• SHIFT LOCK lock other key combinations
• ESCAPE cancel/undo/clear previous/current entry
• CAPS LOCK enable upper-case characters
• TAB move from entry field to another
• CONTROL used in combination with function keys
• RETURN accept current entry
• BACKSPACE delete the character to the left of the cursor
• DELETE delete the current character
• FUNCTION KEYS specific actions, F1=save, F2=load, F3=menu
• ARROW KEYS move from entry field to another
• BREAK/RESET abort entry, return to menu
• NUMERIC KEYPAD for numeric input data

Caring For The Computer System
This section describes appropriate methods for caring for your computer system.

The objective of this section is to

• outline methods of caring for the screen and keyboard
• outline power requirements and safety procedures
• At the end of this section you should be able to
• describe methods of caring for the keyboard and screen
• discuss what screen-burn-out is, and how to prevent it
• connect a computer system and turn it on

Cleaning of the computer system is to be undertaken with the system turned off.

Cleaning the Screen Display Surface
The screen surface should be cleaned using a suitable cleaning agent and cloth. The major concerns are

• anti-static to prevent the attraction of dust and fabric particles onto the screen surface. This attraction reduces the visible contrast and brightness of the display.
• non-smear to reduce reflections and residue film left on the screen surface by the cleaning fluid. Excess cleaning fluid should evaporate without leaving a residue.
• cotton cloth to prevent scratching of the screen surface, and minimize the deposit of lint/fluff by the cloth.

Fig 4: Screen Cleaning Kit

Cleaning fluid in the form of aerosol spray is very good, and the screen surface wiped in a circular motion using a cotton cloth (or lens tissue suitable for cleaning camera lens). Other cleaning systems use tissue wipes that are impregnated with a cleaning agent. The solvent is designed to evaporate quickly, leaving the screen surface smear free. Other properties such as "repelling" dust particles is often claimed in many of the adverts.

Cleaning the keyboard
The surface of the keyboard keys are cleaned in much the same manner as the screen display.

• Care should be taken to prevent excess downward pressure on the keys whilst cleaning.
• Avoid the use of abrasive or corrosive fluids that might etch the letters of the keys.
• Dust is removed by use of portable vacuum cleaner, or little brush which has an air pump attachment.

What is screen burnout?
Screen burnout is a term used to describe damage caused to the inside surface of the screen display. The inner surface of the screen is coated in a phosphorous material that emits light when struck by an electron beam.

If a screen display is static, the electron beam continually strikes the same place on the screen surface, and eventually burns a hole (or wears away) in the phosphorous coating. This might take several days or weeks to occur.

Damage to the screen cannot be repaired. Damage is visible by turning of the display, and inspecting the screen surface closely. If an image can be seen, the screen has suffered damage (i.e, suffers from screen burnout).

The factors that determine how severe the screen burnout is are

• length of time the screen image remains constant
• the brightness and contrast levels of the screen
• the type of phosphorous coating used on the screens inner surface

How is screen burnout avoided?
Screen burnout is avoided by following common sense principles. These are summarized as

• turn down the screen brightness if leaving the machine unattended
• using a "screen saver program"
• switching the monitor off over longer periods
• using an energy star compliant monitor with power saving enabled

A screen saver program detects when the computer is idle, and changes the screen display at periodic intervals so that the displayed image is constantly changing. Most screen saver programs provide a choice of screen images to display, as well as adjusting the amount of idle time necessary before changing the screen display.

When a key is pressed, the screen saver program restores the original screen display. Another common feature of screen saver programs is a password lock, because it is designed for the user to leave the computer unattended for a short period of time (during which another user might try to gain access).

Fig 5: Windows95 Screen Saver Dialog Box

An energy star compliant monitor will switch itself off into low power states when the input signal does not change for a determined time interval. Some modern operating systems like Windows 95 support this mode of operation. In the example below, there are two modes supported, low power mode, where the monitor is still running but the image is not displayed, and shut-down mode where the monitor is turned off.

In enter either mode, the computer sends a special signal to the monitor. The monitor then enters the specified mode of operation. To return to normal, the computer sends another signal to the monitor in order to reactivate it. This is generally caused by the user moving the mouse or pressing a key on the keyboard.

Fig 6: Energy Star Windows95 Dialog Box

Summary
Memory, both in terms of RAM and disk space, is measured in bytes. A byte is a unit of storage and can hold a single character. A Megabyte is one million bytes.

Screen burnout is permanent damage to the inside surface coating of the monitor screen. It can be prevented by the use of screen savers, turning the monitor off during long periods of inactivity, and turning the brightness and contrast down lower.

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© Copyright Brian Brown, 1992-2000. All rights reserved.