COMPONENTS

1. COMPONENTS OF A PERSONAL COMPUTER

2. A typical personal computer has hard, floppy and CD-ROM disks for storage, memory and CPU chips inside the system unit, a keyboard and mouse for input, and a display, printer and speakers for output. Computer systems ranging from a microcomputer to a large supercomputer contain components providing five functions. The arrows represent the direction information flows between the functional units.

3. If you use a desktop computer, you might already know that there isn't any single part called the "computer.". A computer is really a system of many parts working together. The physical parts, which you can see and touch, are collectively called hardware. Software, on the other hand, refers to the instructions, or programs, that tell the hardware what to do

4. The major hardware components of a computer system are: • Central Processing Unit (CPU) • Main Memory • Motherboard • Peripheral Devices

5. CENTRAL PROCESSING UNIT (CPU)? What is Also called as a processor, microprocessor, central processor, “the brains of the computer”, the CPU is the heart of any computer system. It interprets and carries out basic instructions that operate a computer. Central Processing Unit itself consists of three main subsystems; Control Unit, Registers, And Arithmetic and Logic Unit(ALU).

6. Control Unit (CU) The control unit of the CPU contains circuitry that uses electrical signals to direct the entire computer system to carry out, or execute, stored program instructions. The control unit does not execute program instructions; rather, it directs other parts of the system to do so. The control unit must communicate with both the arithmetic/logic unit and memory.

7. Arithmetic & Logic Unit (ALU) Arithmetic logic unit (ALU) is a digital circuit that performs arithmetic and logical operations. An ALU loads data from input registers, an external Control Unit then tells the ALU what operation to perform on that data, and then the ALU stores its result into an output register. The Control Unit is responsible for moving the processed data between these registers, ALU and memory.

8. Arithmetic & Logic Unit (ALU) Arithmetic/logic unit (ALU) performs execution part of the machine cycle. The execution consists of arithmetic (addition, subtraction, multiplication, and division), Comparison (greater than, equal to, or less than) and Logical (AND, OR, NOT).

9. Registers Registers are temporary storage areas for instructions or data. They are NOT a part of memory; rather they are special additional storage locations that offer the advantage of speed.

10. Registers Registers work under the direction of the control unit to accept, hold, and transfer instructions or data and perform arithmetic or logical comparisons at high speed. The control unit uses a data storage register the way a store owner uses a cash register – as a temporary, convenient place to store what is used in transactions.

11. How the CPU Executes Program Instructions? Before an instruction can be executed, program instructions and data must be placed into memory from an input device or a secondary storage device. Once the necessary data and instruction are in memory, the central processing unit performs the following FOUR steps for each instruction: STEP 2: The control unit decodes the instruction (decodes what it means) and directs the necessary data to be moved from memory to the ALU. STEP 3: The ALUexecutes the arithmetic or logical instruction. That is, the ALU is given control and performs the actual operation on the data. STEP 4: The ALUstores the result of this operation in memory or in a register. STEP 1: The control unit fetches (gets) the instruction from memory.

12. STEP 1 & STEP 2 together are called instruction time, or I-time. STEP 3 & STEP 4 together are called Execution time, or E-time.

13. MEMORY Memory is also known as primary storage, primary memory, main storage, internal storage, main memory, and RAM (Random Access Memory). Memory is the part of the computer that holds data and instructions for processing. Although closely associated with the CPU, memory is separate from it. Memory stores program instructions or data for only as long as the program they pertain to is in operation.

14. RAM (RANDOM ACCESS MEMORY) Random-access, commonly known as RAM or simply memory, provides space for your computer to read and write data to be accessed by the CPU. RAM is volatile; data stored in RAM stays there only as long as the computer is running. As soon as the computer is switched off, the data stored in RAM disappears.

15. RAM (RANDOM ACCESS MEMORY) There are two different types of RAM: DRAM (Dynamic Random Access Memory) SRAM (Static Random Access Memory). • SRAM • faster and more reliable than the more common DRAM • doesn't need to be refreshed like dynamic RAM. • Volatile i.e. lose their contents when the power is turned off • DRAM • has memory cells with a paired transistor and capacitor requiring constant refreshing • Volatile i.e. lose their contents when the power is turned off • DRAM • only one transistor and a capacitor are required per bit. • DRAM is used • in main • memory • SRAM • Uses multiple transistors, typically four to six, for each memory cell but doesn't have a capacitor in each cell. • It is used primarily for cache.

16. ROM (READ ONLY MEMORY) Read-Only Memory (ROM) is an integrated-circuit memory chip that contains configuration data. ROM is used in most computers to hold a small, special piece of software: the 'boot up' program. This software runs when the computer is switched on or 'boots up'. The software checks the computer’s hardware and then loads the operating system.

17. ROM (READ ONLY MEMORY) Data stored in ROM is nonvolatile - it is not lost when your computer is turned off. Data stored in ROM is either unchangeable or requires a special operation to change. Examples of ROM are: Programmable ROM (PROM), Erasable Programmable ROM (EPROM) and Electrically Erasable Programmable ROM (EEPROM).

18. PERIPHERAL DEVICES Technically, a computer need only be made up of a CPU and some RAM. But a computer like this would not be much use to anybody – other devices need to be connected to allow data to be passed in and out of the computer. The general name for these extra devices is ‘peripheral devices’. They are usually categorised into input devices, output devices and storage devices.

19. PERIPHERAL DEVICES Output Devices Devices that bring data OUT ofthe computer. Input Devices Devices that bring data INTO the computer. Storage Devices Devices that is capable of STORING information.

20. Input Devices

21. What is input device? • Any hardware devices that sends information to the CPU to • perform a specific function. • It is simply something that is used to interact with, or provide • data to, the computer. • Common input devices: • Keyboard • Pointing devices • Touchpad • Webcam

22. Keyboard A computer keyboard is a peripheral modeled on the typewriter keyboard. One of the most common types of input devices that is used with a computer. Consists of letters, numbers and other types of keys that perform different types of functions by pressing other keys or simultaneous key presses. The most common arrangements in Western countries are based on the QWERTY layout. A computer keyboard is effectively an array of switches, each of which sends the PC a unique signal when pressed.

23. Pointing Devices An input interface that allows a user to input data to a computer. Graphical user interfaces (GUI) allow the user to control and provide data to the computer using physical gestures — point, click, and drag Movements of the pointing device are echoed on the screen by movements of the pointer (or cursor) and other visual changes. While the most common pointing device by far is the mouse, many more devices have been developed..

24. Pointing Devices Types of pointing devices: Mouse Trackball Joystick Pointing stick

25. Touchpad A touchpad or track pad is a flat surface that can detect finger contact. It's a stationary pointing device, commonly used on laptop computers. At least one physical button normally comes with the touchpad, but the user can also generate a mouse click by tapping on the pad. Advanced features include pressure sensitivity and special gestures such as scrolling by moving one's finger along an edge.

26. Webcam Web cams are digital cameras that can be connected to a computer to record video and enable video conferencing capability. Most web cams come with a built-in microphone, though microphones can be purchased separately. Web cam allows you to capture visual input on your machine, though most web cams are used for video conferencing and video chat.

27. OUTput Devices

28. What is output device? • Peripheral hardware connected to the computer, used to • communicate the results of data processing carried out • by a computer system to the outside world. • Common output devices: • Monitor • Printer • Scanner • Projector • Speaker

29. Monitor A monitor or display screen, is an electronic visual display for computers. The term monitor, however, usually refers to the entire box, whereas display screen can mean just the screen. The term monitor often implies graphics capabilities. The most important aspect of a monitor is its screen size. Screen sizes are measured in diagonal inches, the distance from one corner to the opposite corner diagonally. A typical size for small VGA monitors is 14 inches.

30. Monitor The resolution of a monitor indicates how densely packed the pixels are. The more pixels (often expressed in dots per inch), the sharper the image. Most modern monitors can display 1024 by 768 pixels. Some high-end models can display 1280 by 1024, or even 1600 by 1200.

31. Monitor Some factors that determine a monitor's quality are as follow: bandwidth: The range of signal frequencies the monitor can handle. This determines how much data it can process and therefore how fast it can refresh at higher resolutions. refreshrate:How many times per second the screen is refreshed (redrawn). To avoid flickering, the refresh rate should be at least 72 Hz. dot pitch:The amount of space between each pixel. The smaller the dot pitch, the sharper the image. convergence:The clarity and sharpness of each pixel.

32. Printer A printer is a peripheral which produces a text and/or graphics of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most newer printers, a USB cable to a computer which serves as a document source. In addition, a few modern printers can directly interface to electronic media such as memory cards, or to image capture devices such as digital cameras, scanners; some printers are combined with a scanners and/or fax machines in a single unit, and can function as photocopiers.

33. Scanner A scanner is an output device that scans documents such as photographs and pages of text. When a document is scanned, it is converted into a digital format. This creates an electronic version of the document that can be viewed and edited on a computer. Most scanners are flatbed devices, which means they have a flat scanning surface. This is ideal for photographs, magazines, and various documents. Most flatbed scanners have a cover that lifts up so that books and other bulky objects can also be scanned. Another type of scanner is a sheet-fed scanner, which can only accept paper documents. While sheet-fed scanners cannot scan books, some models include an automatic document feeder which allows multiple pages to be scanned in sequence.

34. Scanner Scanners work in conjunction with computer software programs, which import data from the scanner. Most scanners include basic scanning software that allows the user to configure, initiate, and import scans. Scanning plug-ins can also be installed, which allow various software programs to import scanned images directly. For example, if a scanner plug-in is installed for Adobe Photoshop, a user can create new images in Photoshop directly from the connected scanner.

35. Speaker Speakers are the computer component responsible for outputting data in audio format. Computer speakers typically packaged with computer systems are small, plastic, and have mediocre sound quality. Some computer speakers have equalization features such as bass and treble controls. The internal amplifiers require an external power source, usually an AC Adapter. Some computer displays have rather basic speakers built-in. Laptops come with integrated speakers. Unfortunately restricted space available in laptops means these speakers usually produce low-quality sound.

36. STORAGE Devices

37. What is storage device? • A storage device is a hardware device capable of storing • information. • There are two storage devices used in computers; a primary storage device such as computer RAM and a secondary storage device such as a computer hard disk drive. • Common storage devices: • Hard drive • USB • CD& DVD • Memory cards

38. Types of Storage There are three types of data storage: Primary data storage Secondary storage devices Tertiary storage devices The classification of computer storage devices is made based on the task performed by the device.

39. Primary Storage Primary memory, often called main memory, is the storage device that is directly connected to the CPU and store data temporarily during execution. i.e. CPU can directly access primary storage and stores instruction and data for execution/processing. Primary memory is synonymous with random-access memory (RAM). As a computer performs its calculations, it is continuously reading and writing (i.e., storing and retrieving) information to and from RAM. There are two types of primary memory: RAM (Random Access Memory ) ROM (Read-Only Memory)

41. Secondary Storage Secondary memory, also called auxiliary memory or mass storage, consists of devices not directly accessible by the CPU. Hard drives, CD ROM, DVD ROM, USB mass storage devices, floppy disks are widely used for secondary storage. The input and output of these devices is much slower than for the semiconductor devices that provide the computer's primary memory. Most secondary storage devices are capable of containing much more information than is feasible for primary memory (hence the use of the term "mass storage" as a synonym for secondary memory).

42. Secondary Storage Essential feature of secondary memory is that it is non-volatile. This means that data is stored with or without electrical power being supplied to the device, as opposed to RAM, which can retain its data only so long as electrical power is present. The most popular examples of secondary device is the Hard disk and USB

43. Secondary Storage: Hard Drive One of the most important of the secondary types of computer data storage devices. It is non-volatile. Data are magnetically read from and written to the platter by read/write heads that float on a film of air above the platters. Hard disks are typically about a million times slower than memory.

44. Secondary Storage: CD & DVD The data is stored on the CDs in optical format. Backup can be stored on the CDs. The format of storing data in the digital versatile discs (DVD) is similar to that of a compact disc. The difference lies in the storage capacity. There is six times more storage space in the DVD’s as compared to the CD’s. Like the CD’s, DVD’s are also used as backup device.

45. Secondary Storage: USB The Universal Serial Bus (USB) are very small in size, but have very large memory space. USB is non-volatile and data can be rewritten on them.

46. Secondary Storage: Memory cards Data is stored in digital format on the memory cards. They can be used in various electronic devices from hand held computers, mobile phones, cameras, etc. They are also rewritable. Although they are small in size, they can store a high amount of data.

47. Differences between Primary Memory and Secondary Memory:

48. Tertiary Storage A much slower way of supplying data to the CPU of a computer than secondary storage or RAM. Often used for archived data, or very large stores of data. Each tape or disc is retrieved by a robotic arm system, transferred to a device that reads the data, and then is replaced by the arm when data transfer has been completed; this data is often copied to secondary storage before use. Typical examples include tape libraries and optical jukeboxes.

49. Tertiary Storage When a computer needs to read information from the tertiary storage, it will first consult a catalog database to determine which tape or disc contains the information. Next, the computer will instruct a robotic arm to fetch the medium and place it in a drive. When the computer has finished reading the information, the robotic arm will return the medium to its place in the library.