NOTE ON FORM ONE ABOUT THE SECOND TOPIC Computer systems1.pptx

hIGH SCHOOL NOTES

1. Today’s Topic – COMPUTER SYSTEMS We will learn: Description of a computer system. Input Devices The Central Processing Unit(C.P.U). Output Devices Secondary storage devices and Media Power supply and peripheral device interfacing Basic computer setup and cabling Computer software Criteria for selecting a computer system

2. Definition of terms : A System is the collection of entities that collectively work together to achieve a stated goal. Description of a computer system A Computer system is a collection of 3 entities namely; Hardware , Software and Liveware that work together to receive, process manage and present information in a meaningful format. Hardware – refers to physical or tangible components that make up a computer system. We have 4 categories of hardware namely; input devices , central processing unit , output devices and storage devices . Software – refers to a set of instructions that direct a computer on what to do.

3. Liveware – is an informal term that refers to the human users attachment to the computer. Also called wetware or grayware . Are computer users who command a computer to perform a task. Classification of computer Hardware Computer hardware is classified into 4 categories: 1. Input devices – are devices used convert user input which is in human readable form to machine language that the a computer can understand and process. Input devices are classified as follows; keying devices, pointing devices, scanning devices . A) keying devices The following are types of keying devices: Traditional keyboards – is the most common type of keying device.

4. Flexible keyboard – is more portable keyboard that can be folded and packed into a bag. Ergonomic keyboard – is specially designed to provide comfort and prevent wrist strain . Keypad – is a small keyboard used on portable devices i.e PDAs, laptops and mobile phones. Braille keyboard – is designed for use by the blind. It consists of keys identified by raised dots.

5. B) Pointing devices Pointing devices are used for controlling a pointer on the screen. The following are types of pointing devices: Mouse Types of mice Standard mouse/traditional mouse Optical mouse – does not have any moving parts. Uses light technology to capture input. Cordless /wireless mouse – is a battery powered mouse that uses radio or infrared waves instead of being physically connected to the system unit.

6. Trackball It works just like a mouse only that its ball is located at the top Joy stick Is an input device used to play computer games by controlling a pointer on the screen. The information is made available on: Light pen and stylus – operates by detecting commands. C) Scanning devices Scanning is capturing data from an object and converting it into digital format. Scanning devices can be classified according to the technology used to capture data, which include: optical scanners & magnetic scanners .

7. 1. Optical scanners Optical scanners capture data using optical/light technology. Examples of optical scanners Optical mark recognition scanners(OMR) OMR scanners detects marks made on a piece of paper using ink or pencil. They are used to mark multiple choice questions. Optical bar recognition(OBR) Optical barcode recognition scanners are used in supermarkets to capture barcodes or universal product code. n/b Barcodes hold manufacturer’s details and the product code but not price details because prices vary from one place to another. Optical character recognition scanners(OCR) OCR scanners are used to read typewritten, printed or handwritten characters and converts the images into softcopy.

8. 2. Magnetic scanners This are used to capture data written using magnetic ink. Examples include; Magnetic Ink Character Recognition(MICR) and card readers Other Input Devices Digitizers/ a graphic tablet Allows users to draw an image using a stylus. Digital cameras Captures images and stores them in digital form. Touchscreen Voice input/microphone Enters data in form of speech into the computer. Mostly used by the physically challenged users(blind). Disadvantages of voice input are: does not fully support speech related aspects i.e accents, inflections & tones. Interactive whiteboard/ Smartboard Is a large interactive display that connects to a computer and users can write using a pen or a finger. Smartboards are used in classrooms, corporate boardrooms, seminars & broadcasting studios.

9. The central processing unit(CPU) The CPU also known as the processor is the brain of the computer where all processing activities are carried out. The CPU consists of 3 functional elements namely; the control unit , the arithmetic and logic unit(ALU) and the main memory . Control Unit – coordinates all processing activities in the CPU. Arithmetic and Logic Unit(ALU) – It is where all arithmetic and logical operations are carried out. Main/Primary Memory – is storage that is directly accessible by the processor. Classification Of Computer Main Memory It is classified into; Read Only Memory(ROM), Random Access Memory(RAM) & Special Purpose Memories .

10. Results of processing Data to be processed Data to be processed Output to be stored

11. 1. Read Only Memory(ROM) ROM is used to store programmed instructions and data permanently. Characteristics of ROM It is read only memory where you cannot change its contents It is non-volatile i.e its content is not lost when the computer is switched off. It is a permanent storage.

12. Types Of Read Only Memory Mask Read Only Memory(MROM) – Once the content is written on it by the manufacturer it cannot be changed. Programmable Read Only Memory(PROM) – this allows the user to alter it only once after the content is written on it. Erasable Programmable Read Only Memory(EPROM) – this can be erased by exposing it to light. Electrically Erasable Programmable Read Only Memory(EEPROM) – can be erased and reprogrammed using electricity

13. 2. Random Access Memory(RAM ) Also known as working storage is used to hold instructions and data needed by currently running applications. The size of RAM enhances the speed and performance of the processor. The more RAM that is available the more programs can run at the same time. Characteristics of RAM It is both read and write RAM is temporary( volatile ) storage because its content disappears when the computer is switched off. Its content is user defined i.e the user dictates what is to be contained in RAM. RAM is classified into 2 types; Static and Dynamic RAM. Static RAM – is a fast type of memory located inside the processor. Dynamic RAM – is a relatively slower type of RAM compared to SRAM. It requires periodic recharging(refresh) to maintain its data storage.

14. special purpose memories These memories include buffers , registers , & cache memory . Cache Memory Is a fast type of RAM. There are 3 types of cache memory namely: level 1, level 2 & level 3 . Level 1 cache – also known as primary cache located inside the microprocessor. Level 2 cache – also known as external cache located inside the microprocessor or mounted on the motherboard. Level 3 cache – is the latest type of cache that work with L2 cache to optimize system performance. Buffers – are special memories that are found in Input/output devices. Input data is held in the input buffer , while, processed output is held in output buffer . Registers – hold one piece of data at a time and are inside the CPU. Examples of registers are; Accumulator, Instruction register, Address register, Storage register .

15. Accumulator – this temporarily holds the results of the last processing step of the ALU. Instruction register – this temporarily holds an instruction just before it is interpreted into a form that CPU can understand. Address register – temporarily holds the next piece of data waiting to be processed. Storage register – temporarily holds a piece of data that is on its way to and from the CPU and the main memory. Overall functional organization of the CPU The Arithmetic and Logic Unit, The Control Unit and the Main Memory use electrical pathways called buses to interact. There are 3 types of buses namely; control, address & data bus . Control bus – is the pathway for all timing & controlling functions sent by the control unit to other parts of the system. Address bus – is the pathway used to locate the storage position in memory where the next instruction data to be processed is held. Data bus – is pathway where the actual data transfer takes place.

16. Memory Capacities Memory and storage capacities is measured in special units called bytes . Memory Quantities Memory Unit Conversion SIZE Bytes 1024bytes=1KB SMALLEST Kilobytes 1024KB=1MB Megabytes 1024MB=1GB Gigabytes 1024GB=1TB Terabytes 1024TB=1PB Petabytes LARGEST

17. Computer Processor Speed Processor speed is measured in clock cycles per second. This is the number of times per second the processor can carry out one or more instructions. It is measured in units called Hertz(HZ) . Processor Speed Speed Unit Conversion Hertz 1000Hz=1KHz Kilohertz 1000KHz=1MHz Megahertz 1000MHz=1GHZ Gigahertz

18. Types of processors There are 2 categories of processors classified according to the number of instruction set. Complex instruction set computer(CISC) processor – is made up of a large number of complex instructions set. Reduced instruction set computer(RISC) processor – uses fewer instructions set compared to CISC.

19. Output Devices Output devices are devices used to give out information produced after data processing. They are classified into 2 categories namely softcopy and hardcopy output devices. Softcopy output devices Soft copy refers to intangible output that can be seen or heard i.e screen display and sound. Examples of such devices include monitors, projectors speakers(sound output) and light emitting diodes(LED). Monitors/computer screens Also called Visual Display Unit (VDU) displays information in the form of text, pictures and video. There are 3 types of monitors namely; Cathode Ray Tube(CRT) , Liquid Crystal display(LCD) and Gas Plasma Display(GPD) monitors. GPD and LCD are flat-panel displays and are less bulky, consume less power and have little eyes strain effect as compared to CRT monitors. There are 2 technologies used to make LCDs, Passive matrix and Active matrix

20. In passive matrix LCDs create images by scanning the entire screen. This requires little power but have poor clarity. In Active matrix – displays are made using thin film transistors (TFT) technology. This consumes more power but offer better clarity than passive matrix. GDP resembles LCD s only that they make use of gas instead of liquid crystals and also images do not suffer from angle distortion . Monitor Display Terms Pixel – stands for picture elements, are tiny dots which are used to form the images displayed on the screen. Pixel has 3 colours : red, green & blue. Colour depth – is the number of colours which can be displayed by a pixel. Resolution - is the number of pixels per inch on the screen (usually given in dots per inch). The higher the resolution the more the number of pixels, hence clearer the images. Display size – is measured in inches as the diagonal length of the screen.

21. Video adapters – used to enable a monitor to display output. It determines the clarity and the resolution of the monitor. Examples of video adapters Colour graphics adapter(CGA) – oldest type that displays images up to 16 colours . Enhanced graphics adapter(EGA) – displays in 16 colours but was an improvement of CGA. Video garphics array(VGA) - displays text, graphics and video using 256 colours . Super video graphics array(SVGA) – displays text and graphics using more than 16 million colours . Extended graphics array(XGA) – has a resolution of up to 1024*768 pixels. Super extended graphics array(SXGA) – has a resolution of up to 1280*1024. Ultra extended graphics array(UXGA) – is the latest and highest standard.