The Computer System

1. The Computer System By LoWing Tat (10)

2. 1. System Unit 1.1 Central processing unit(CPU) 1.2 Memory

3. 1.1 Central processing unit(CPU) • 1. What is Central processing unit(CPU)? • 2. What does CPU look like? • 3. What does CPU contains? • 4. Where does the microprocessor gets its instructions? • 5. What makes one microprocessor perform better than another? • 6. What do MHz and GHz have to do with computer performance?

4. 1. What is Central processing unit(CPU)? • Central processing unit (CPU) accepts and executes sequentially the instructions stored in the main memory. • It is an integrated circuit designed to process instructions. • It is the most important component of a computer.

5. 2. What does CPU look like? • Looking inside a computer, you can usually identify the microprocessor because it is the largest chip*1 on the motherboard. • Depend on the brand and model, a microprocessor might be housed on 1. SEC cartridge 2. Square PGA *1 Chip : The term "chip", "computer chip" and "microchip" originated as technical jargon for Integrated Circuit (IC), which is a super thin slice of semi-conducting material packed with microscopic circuit elements such as wires, transistors, capacitors, logic gates and resistors.

6. 3. What does CPU contains? • The CPU contains the control unit (CU) , the arithmetic and logic unit (ALU) and several registers.

7. Control Unit (CU): • The function of the control unit (CU) is to direct all operations occurring within the computer. • It is responsible for: 1. sending and receiving control signals to and from peripheral devices 2. interpreting the instructions stored in main memory 3. regulating the timing of all operations performed within the CPU 4. sequencing the instructions to be executed 5.controlling the flow of data between the CPU, main memory and peripheral devices.

8. The control unit contains an instruction register (IR) *2, an instruction decoder*3 and a program counter (PC) *4 *2 Instruction Register : A register is a storage unit which has a specified storagecapacity. It is used for temporary storage of instructions, data and addresses. An instruction register(IR) is a register that holds the current instructions fetched from main memory. *3 Instruction decoder : An instruction decoder is a logic circuit which interprets the current instructions stored in the instruction register. *4 program counter(PC) : A program counter(PC) is a register which holds the address of the next instruction to be accessed after the current instruction has been fetched.

9. Arithmetic and Logic Unit (ALU): • ALU performs arithmetic operations, such as addition, subtraction, multiplication, division etc.. • It also performs logical operations such as decision making. For instance, comparing two numbers to see if they are the same. • The ALU makes use of registers when performing these operations. • They include an accumulator*5 and a status register*6 *5 Accumulator :An accumulator(ACC) is a register which temporarily holds the intermediate or final result of arithmetic and logical operations. *6 Status Register : A status regidter(SR) describes the status of the current contents of the accumulator and holds a collection of bits.

10. 4. Where does the microprocessor gets its instructions? • The CPU accepts and executes sequentially the instructions stored in the main memory or computer program. • The list of instructions that a microprocessor can perform is called its instruction set. • These instructions are hard-wired into the processor's circuits and include basic arithmetic and logical operations, fetching data, and cleaning registers. • A computer can perform very complex tasks, but it does so by performing a combination of simple tasks from its instruction set.

11. 5. What makes one microprocessor perform better than another? • The performance of a microprocessor is affects by several factors, including clock speed, word size, cache size, instruction set, and processing techniques.

12. 6. What do MHz and GHz have to do with computer performance? • The speed specification that you see in a computer and indicate the speed of the microprocessor clock-a timing device that sets the pace for executing instructions. Most computer ads specify the speed of a microprocessor in megahertz (MHz) or gigahertz (GHz).Megahertz means a million cycles per second. Gigahertz means a billion cycles per second. That means a computer with a 1.3 GHz processor is faster than a computer with a 1 GHz processor or a 933 Mhz processor. • A cycle is the smallest unit of time in a microprocessor's universes. Every action that a processor performs is measured by these cycles. It is important, however, to understand that the clock speed is not equal to the number of instructions that a processor can execute in one second. In many computers, some instructions occur within one cycle, but other instructions might require multiple cycles. Some processors can even execute several instructions in a single clock cycle.

13. 1.2 Memory 1. What is Memory? • The memory includes : 1. RAMand 2. ROM. The RAM holds instructions and data temporary while the ROM holds system programs and data permanently.

14. 1.2.1 RAM • 1. What is RAM? • 2. What does RAM look like? • 3. Why RAM so important? • 4. How does RAM work?

15. 1. What is RAM? • Random access memory(RAM) is a temporary holding area for data, application program instructions and the operating system. • In a personal computer, RA is usually several chips or small circuit boards that plug into the motherboard within the computer's system unit.

16. 2. What does RAM look like? • RAM is usually configured as a series of DIPs soldered onto a small circuit board called a DIMM (dual in-line memory module).

17. 3. Why RAM so important? • RAM is the "waiting room" for the computer's processor. It holds raw data that is waiting to be processed, as well as the program instructions for processing that data. • In addition, RAM holds the results of processing until they can be stored more permanently on disk or tape.

18. 4. How does RAM work? • In RAM, microscopic electronic parts called capacitors hold the bits that represent data. You can visualize the capacitors as microscopic lights that can be turned on or off. A charged capacitor is "turned on" and represents a "1" bit. A discharged capacitors is "turned off" and represents a "0" bit. • Each blank of capacitors holds eight bits(=one byte) of data. A RAM address on each bank helps the computer locate data, as needed, for processing.

19. 1.2.2 ROM • 1. What is ROM? • 2. How is ROM different from RAM? • 3. Why does the computer need rom too?

20. 1. What is ROM? • Read-only memory(ROM) is a type of memory circuit that holds the computer startup routine. • ROM is housed in a single integrated circuit - usually a fairly large, caterpillar DIP package - which is plugged into the motherboard.

21. 2. How is ROM different from RAM? • Whereas RAM is temporary and volatile, ROM is permanent and non-volatile. • ROM circuitry holds "hard-wired" instructions that remain in place even when the computer power is turned off.The instructions in ROM are permanent, and the only way to change them to replace the ROM chip.

22. 3. Why does the computer need rom too? • When you turn off your computer, all instructions will be cleaned. It is empty and doesn't contain instructions for the microprocessor to execute while you turn on your computer again. • ROM contains a small set of instructions called the ROM BIOS(basic input/output system) in the CMOS memory(complementary metal oxide semiconductor memory) which is a type of chip that requires very little power to hold data. These instructions tell the computer how to access the hard disk,the computer can understand your input,display output,run software, and access your data.

23. 2.Periperal devices 2.1 Input devices 2.2 Output devices 2.3 Storage devices

24. 2.1 Input devices • Input devices accept input data and pass them to the CPU unit to process. • There are various input devices to fit different tasks, for example 1. Keyboards , 2. Pointing Devices ( i. Mouse, ii. touch screen, iii. light pen, iv. digitizer ), 3. Scanning devices (i. image scanner, ii. fax machine, iii. bar-code scanner, iv. magnetic ink character recognition, v. optical character recognition, vi. optical mark recognition ), 4. voice - input devices , 5. Chinese hand writing recognition device

25. 1. Keyboards • Keyboards are the most commonly used input devices. User enter data by pressing the corresponding keys on the keyboard. • There are several types of cables connecting between Keyboard and computer : 1.wires , 2. infrared(IR) , 3. FM microwave , 4. Blue Tooth etc. • There are 3 kinds of keyboard port : 1. AT , 2. PS/2 , 3. USB It is designed for the purpose for saving time and reducing errors.

26. 2. Pointing Devices • Pointing devices allow users to relocate the pointer on the screen, and then select data or a command. Pointing Devices containing: • i. Mouse, • ii. touch screen, • iii. light pen, • iv. digitizer

27. i.) Mouse • A mouse is a kind of pointing device that allows a user to control the mouse pointer. • The most common type of mouse has a small ball on the bottom and is attached with a cord to the system unit.The ball senses the movement of the mouse and the mouse pointer will move according to the movement of the mouse.On top of the mouse, there are two or more buttons. The user can perform an action such as selecting an item by pressing the button. • There are several types of cables connecting between mouse and computer : 1.wires , 2. infrared(IR) , 3. FM microwave , 4. Blue Tooth etc. • There are 3 kinds of mouse port : 1. AT , 2. PS/2 , 3. USB

28. ii.) touch screen • A touch screen allows a user to enter data by touching the touching the screen with a finger.It is faster than typing on a keyboard or using a mouse. • However, it is not suitable for inputting a large amount of data. A touch screen is commonly used in public services such as information seeking.

29. iii.) light pen • A light pen is a device connected to a computer, that when pointed at a computer display senses whether or not the spot is illuminated. It then sends the information to the computer.

30. iv.) digitizer • A digitizer can be used to trace or copy a drawing or a photograph. The shape is then converted to digital signals that are transmitted to the computer

31. 3. Scanning devices • Scanning devices record image of text, drawings or special symbols in their original forms. The images are then converted to digital data that can be processed by the computer. Using scanning devices eliminates human operation, thereby increasing efficiency and reducing human error. • Scanning devices containing : • i.) image scanner • ii.) fax machine • iii.) bar-code scanner • iv.)magnetic ink character recognition • v.) optical character recognition • vi.) optical mark recognition

32. i.) image scanner • An image scanner captures images or text onto the computer. • The scanner will digitizes the input data so that they can be processed by the computer. Once the image or text are digitized, they can be modified and merges with other text or images.

33. ii.) fax machine • Fax machine communications system for the electrical transmission of printed material, photographs, or drawings. Facsimile transmission is accomplished by radio, telephone, or undersea cable.

34. iii.) bar-code scanner • A bar code scanner is a photoelectric scanner that reads the bar codes printer on product containers. • A bar code scanner consists of a set of vertical lines with different widths. The bar codes canner identified a bar code by the reflected light pattern from the bar code lines. The most familiar bar code system is the Universal Product Code(UPC). The UPC can be translated into a ten-digit number that identifies a product, You can easily find a bar code scanner at a point-of-sale terminal in a supermarket.

35. iv.) magnetic ink character recognition • A character recognition system using special ink and characters which can be magnetised and read automatically. • MICR is used almost exclusively in the banking industry where it is used to print details on cheques to enable automatic processing.

36. v.) optical character recognition • An optical character reader(OCR) can recognise characters with special typefaces. • An OCR uses a light source to read the shape of a character and converts the image into digital data. The OCR then compares the pattern read with a predefined pattern in memory. The read character is assumed to be the character whose stored pattern most closely matches the read pattern. The OCR is commonly used in department stores to read retail price tags.

37. vi.) optical mark recognition • A technique that enables marks made in predetermined positions on computer-input forms to be detected optically and input to a computer. • An optical mark reader shines a light beam onto the input document and is able to detect the marks because less light is reflected back from them than from the paler, unmarked paper.

38. 4. voice-input devices • Users can enter data or give commands to the computer with spoken words through voice - input devices. • Through a microphone and digitise them, so that they can be processed by the computer. The command may be performing a specific action such as saving a document or operating industrial machines.

39. 5. Chinese hand writing recognition device • Users write a character with a special device such as a special pen or writing pad. • The system recognizes the shape of the written character and matches it to the most similar character. Then a list of these characters is shown for selection.

40. 2.2 Output devices • Output devices are used to present the information to users. • There are various output devices to fit different tasks, for example, • 1. Visual display unit • 2. Printers (i. Laser Printers, ii. Ink-jet Printers, iii. Dot-matrix Printers) • 3. Plotters • 4. Voice-output device

41. 1. Visual display unit • Basically, a VDU is a monitor which looks like a television. It can be used to display images such as text, graphics and even video films or animation. • A pixel is the smallest unit on the VDU that can be turned on and off or made different shades. The most important features of a monitor are its screen size, number of maximum displayable colours and resolution. the resolution of the image on the VDU depends on the density of the pixels, that is, the number of rows and columns of pixels. There are two kinds of VDUs. • cathode-ray tube (CRT) and liquid crystal display (LCD) monitors.

42. 2. Printers • The image output on a monitor are often referred to as soft copy, while that on paper is called hard copy. • Printers are commonly used output devices that output image on paper. In general, there are two types of printers: impact printers and nonimpact printers. Impact printers transfer characters onto paper by striking the paper, ribbon and character together. Nonimpact printers output images on paper without physically touching thepaper. Nowadays, only one type of impact printers, dot-matrix printers are used. • Printers are containing : • i.) Laser Printers • ii.) Ink-jet Printers • iii.) Dot-matrix Printers

43. i.) Laser Printers • A laser printer uses laser beams to create images. Laser printers can produce high quality images at high speed. They are commonly used to produce high-quality hard copies. Laser printers can print on paper and transparencies.

44. ii.) Ink-jet Printers • An ink-jet printer sprays droplets of ink onto the paper or transparences through nozzles to form characters and images. Ink-jet printers are reliable and quiet. They are suitable for printing graphics.

45. iii.) Dot-matrix Printers • A dot-matrix printer prints images using a series of wire pins on a print head. A small dot is printed by striking a wire pin again an inked ribbon. These small dots form different characters and images. • Dot matrix printers are noisy, and the printing speed and output quality are fair. However, many organizations use dot-matrix printers to print documents with a large amount of data, such as, bills and invoices.

46. 3. Plotters • Plotters are used to produce high-quality line drawing such as maps, charts, building plans and circuit diagrams. • They can produce high-quality multicolour documents and also documents that are larger in size than most printers can handle. There are three main types of plotters: pen, ink-jet and electrostatic plotter. • Plotters create plots by moving a pen or pencil over drafting paper. Ink-jet plotters create line drawings and solid-colour output by spraying droplets of ink onto paper. Lastly, electrostatic plotters use electrostatic charges to create images made up of tiny dots on specially treated paper.

47. 4. Voice-output device • Instead of reading the soft copy and hard copy, users can hear the information over speakers, headphones, telephones, voice dictionaries and so on.

48. 2.3 Storage devices • Storage devices is storage separate from the CPU. It can hold data and programs permanently for future use. • It is necessary because main memory can be used only temporarily, and users may want to store the data they have used or the information they have obtained from processing. Furthermore, main memory is limited in size, while storage can store as much data as necessary. • There are including : • 1. Floppy disk, • 2. hard disk, • 3. magnetic tape • 4. optical disk

49. 1. Floppy disk • A floppy disk, often called diskette, is a flat, circular piece of plastic that rotates within a jacket. The plastic is coated with a metal oxide film. • Data and programs can be stored as magnetic spots on the film. It is 3.5-inch and provides 1.44 MB storage.

50. 2. Hard Disk • A Hard disk consists one or more metallic platters. Each side of the platters is coated with a metal oxide film, and data can be stored as magnetic spots on the film.