2. We defined a computer as an electronic device that accepts inputs, processes these inputs and gives an output, based on the variable instruction given to it. A computer is made up of a number of parts; some connected to the system unit (peripheral devices) while others are embedded into the system unit (hardware and software). It’s the combination of these devices that make a computer function properly.

3. CATEGORISATION OF COMPUTER SYSTEMS Broadly speaking, computer categorisation refers to the distinction made between computers based on their mode of operation on data or the type of data they process, as they execute their INPUT, PROCESS AND OUTPUT mechanisms. Other classifications, based on size, purpose and function largely fall into these broad categories.

4. Computers are categorised as ANALOGUE, DIGITAL or HYBRID.

5. ANALOGUE COMPUTERS These are computers that process analogous data. Analog data can take on any value within a continuous range. They measure continuously at extremely high speeds and as a result, their results are usually approximations. They are special purpose computers commonly used in manufacturing process control and weather prediction.

6. Analogue computers are represented using a continuous wave form.

7. Analog data has 3 main characteristics; FREQUENCY (Pitch), which refers to the number of times per second the wave form repeats (measured in Hertz), AMPLITUDE (Volume) referring to the maximum height of the wave or strength of the signal (expressed in volts) and PHASE referring to the rate at which a signal changes in relation to time (expressed in degrees). The higher the amplitude, the stronger or louder the signal is.

8. Analogue computers have largely been made obsolete for general purpose mathematical tasks and data processing by digital computers. The Ministry of Information and Telecommunication Technology (Uganda) has come up with a policy on digital Migration for television broadcasting in order to improve signal quality. By the year 2015, Uganda communication will entirely be digital.

9. “The shift in Uganda’s broadcasting sector from analogue broadcasting to digital broadcasting technologies is set to revolutionize the broadcasting industry in the same way when Compact Disc (CDs) and or Digital Video Disc (DVDs) improved the music and videos industry when they replaced the old analogue audio and videocassettes. This change on the whole is driven by digitization which has lead to convergence of technologies

10. DIGITAL COMPUTERS A digital computer is a computer that performs calculations and logical expressions with quantities expressed as digits or numbers usually in the binary number system. Computer operations work on the basis of electrical inputs that can attain two states of ON = 1 and OFF = 0.

11. Therefore, digital data can take on only a finite set of discrete values.

12. Digital Processing has consumed all aspects of society today, ranging from computers to home appliances such as TVs, clocks and microwaves.

13. HYBRID A hybrid – is a thing made by combining two different elements. In terms of computing, hybrid computers have features of both analogue and digital computers. This means that they can process both analogue and digital data. This type of computer is used extensively in process control, as they provide good precision, that can be attained by analogue computers and greater control that is possible with digital computers.

14. COMPUTER CLASSIFICATION BY SIZE Computers can as well be classified according to their size; from the smallest (micro computer) to the largest (super computer)

15. SUPER COMPUTERS They are the fastest, most expensive and powerful computers. They are employed to execute complex applications that require immense amounts of memory and mathematical calculations. Application areas of super computers include; weather forecasting, animated graphics, fluid dynamics, petroleum exploration, defence and systems design and analysis and nuclear energy research.

16. They produce a lot of heat because of their enormous size. Special cooling systems should be in place to cool down the system. Typical examples of super computers include; NASA’S COLUMBIA SUPER COMPUTER, and IBMS’ SEQUOIA super computer found at Lawrence Livermore National Laboratory.

17. The Sequoia Super Computer

18. Super computers are very expensive, priced from $2 million to about $20 million depending on the specification. They occupy huge spaces, have high processing speeds and use a lot of electricity. All their physical attributes are typical characteristics of First generation computers.

19. MAINFRAME COMPUTERS Main frame computers are almost similar to super computers; the main difference being that super computers are stronger and more expensive. They contain one to 16 CPU’s or even more. Its processing speeds range from 80 to 550 MIPS

20. Super computers and mainframes are almost similar in shape and sometimes speed; the main difference being that super computers channel all its power into executing a few programs as fast as possible, whereas mainframes uses its power to execute multiple programs simultaneously. MARK I and IBM 704 Mainframe are examples of mainframe computers

21. MINI COMPUTERS Mini computers are significantly smaller than mainframe computers. According to Ronald E Anderson (1972), mini computers have smaller memory modules, restricted instruction sets and don’t necessarily come with peripheral devices. Webopedia (2012) says that mini computers lie between workstations and Mainframe computers.

22. It is a cheaper version of the mainframe. They are also used in scientific laboratories, engineering plants and in manufacturing process control. They can as well be used for office work such as word processing, spreadsheets and database management.

23. MICRO COMPUTERS Microcomputers are computers that use a microprocessor for its central processing unit As earlier noted, micro computers are categorised as 4 th generation computers as compared to 1st generation (that used vacuum tubes for internal circuitry), 2 nd generation (that used transistors) and third generation (that employed Integrated circuits for internal circuitry).

24. THE PROCESSOR

25. Due to advanced microprocessor technology, we have seen cheaper and smaller computers, and therefore more accessible technology. Because Micro computers are small and affordable, they are the most common form of computer used in small businesses, offices, training institutions, military, and in the construction sector to name a few. Examples of micro computers include; Desktop computers, Notebooks or Laptops and Personal Digital Assistants (PDAs)

26. MICRO COMPUTERS

27. CLASSIFCATION BY FUNCTION This classification is based on how computers are used; they can be Stand-alone, Networked, Rea- Time or Integrated systems.

28. STAND-ALONE COMPUTERS Stand-Alone computers can be a desktop or a laptop computer that is used on its own, without requiring a connection to a local area network (LAN) or a wide area network (WAN).

29. NETWORKED COMPUTERS These are two or more computers that are connected together to form a computer network with the aim of sharing resources (hardware and software resources). Networked computers are usually interconnected through a communication medium (physical or wireless communication medium).

30. NETWORKED COMPUTERS

31. REAL-TIME SYSTEMS REAL TIME systems are computers that execute tasks under a time constraint. The correctness of the system isn’t entirely dependant on the logical results of the computation, but also on the time at which the results are produced.

32. Such computer systems employ a number of sensors (for detecting slight changes in parameters), conditioning circuits (for converting sensor output to the desired state) and real time software. Examples of Real time systems include; Air traffic control Systems, Automobile Braking Systems, Networked Multimedia Systems, and Command Control Systems.

33. INTERGRATED SYSTEMS Integrated Systems is a computer network that links together different computing systems and software applications physically or functionally to act as a whole. It can also be defined as a collection of distinct elements or components that have been built into a single unit.

34. This interconnection allows for common access to sensor information and command and control. For better efficiency especially in terms of security, Integrated Systems are designed in such a way as to enforce independence, rather than inter-dependence. This means that failure of one system unit doesn’t affect the other systems.

35. CLASSIFICATION ACCORDING TO PURPOSE Computers can also be classified according to the tasks they perform. Computers can be General Purpose or Special Purpose.

36. GENERAL PURPOSE COMPUTERS These computers are designed to be able to deal with a number of different tasks or problems, and should be able to respond to a number of programs written for different tasks. They are also able to store a number of software programs and respond appropriately, for example, such computers can do word processing, spreadsheets, accounting, data and information management depending on the users needs.

37. SPECIAL PURPOSE COMPUTERS As the name implies, such computers are designed to perform one specific task. A specific set of limited instructions is embedded into the computer system at the manufacturing stage. Therefore, these highly specialised computers and are very efficient at doing a specific task.

38. They are usually referred to as ‘Dedicated Computers’, because they are tied to a specific task. Examples of special purpose computers include Robots used in specific manufacturing tasks, and electronic calculators that do arithmetic only.