Computer Concept Lecturer: Jing Liu Email: [email protected] Homepage: http://see.xidian.edu.cn/faculty/liujing Textbook E. Balagurusamy, Fundamentals of Computers, Mc Graw Hill. Grading Final exam: 70% Others: 30% Content 1. Understanding the Computer 2. Computer Organisation and Architecture 3. Memory and Storage Systems 4. Input Devices 5. Output Devices 6. Computer Codes 7. Computer Arithmetic 10. Computer Software 11. Operating Systems 12. Microsoft Software 13. Programming Languages 14. Data Communications and Networks 15. The Internet and World Wide Web What’s a Computer? A computer is an electronic machine that takes input from the user, processes the given input and generates output in the form of useful information. What’s a Computer? Input: data, programs, user reply Data: the raw details that need to be processed to generate some useful information. Programs: the set of instructions that can be executed by the computer in sequential or nonsequential manner. User reply: the input provided by the user in response to a question asked by the computer. What’s a Computer? A computer includes various devices: Central Processing Unit (CPU) Monitor Keyboard and Mouse What’s a Computer? The unique capabilities and characteristics of a computer: Speed Storage capacity Accuracy Reliability Versatility Diligence What’s a Computer? Limitations: Garbage-In, Garbage-Out Dumb machine Evolution of Computers Manual Computing Devices: Sand table, Abacus, … Automated Computing Devices: difference engine, analytical engine, Colossus, … Charles Babbage: A professor of mathematics a the Cambridge University is considered to be the father of modern computer. Generations of Computers First Generation Computers • Employed during the period 1940-1956 • Used the vacuum tubes technology for calculation as well as for storage and control purpose. • Advantages: (1) Fastest computing devices of their time; (2) These computers were able to execute complex mathematical problems in an efficient manner. Generations of Computers •Disadvantages: (1) The functioning of these computers depended on the machine language. (2) There were generally designed as special-purpose computers. (3) The use of vacuum tube technology make these computers very large and bulky. (4) They were not easily transferable from one place to another due to their huge size and also required to be placed in cool places. (5) They were single tasking because they could execute only one program at a time. (6) The generated huge amount of heat and hence were prone to hardware faults. Generations of Computers • • • Second Generation Computers Employed during the period 1956-1963 Use transistors in place of vacuum tubes in building the basic logic circuits. Advantages: (1) Fastest computing devices of their time; (2) Easy to program because of the use assembly language; (3) Could be transferred from one place to other very easily because they were small and light; (4) Require very less power in carrying out their operations; (5) More reliable, did not require maintenance at regular intervals of time. Generations of Computers •Disadvantages: (1)The input and output media were not improved to a considerable extent (2) Required to be placed in air-conditioned places (3) The cost of these computers was very high and they were beyond the reach of home users (4) Special-purpose computers and could execute only specific applications Generations of Computers Third Generation Computers • Employed during the period 1964-1975 • Use of Integrated Circuits • Advantages: (1) Fastest computing devices; (2) Very productive; (3) Easily transportable from one place to another because of their small size; (4) Use highlevel languages; (5) Could be installed very easily and required less space; (6) Can execute any type of application. (7) More reliable and require less frequent maintenance schedules. Generations of Computers Disadvantages: (1)The storage capacity of these computers was still very small; (2) The performance of these computers degraded while executing large applications, involving complex computations because of the small storage capacity; (3) The cost of these computers was very high; (4) They were still required to be placed in airconditioned places. Generations of Computers Fourth Generation Computers • Employed during 1975-1989 • Use of Large Scale Integration technology and Very Large Scale Integration technology • The term Personal Computer (PC) became known to the people during this era. Generations of Computers Advantages: (1) Very powerful in terms of their processing speed and access time; (2) Storage capacity was very large and faster; (3) Highly reliable and required very less maintenance; (4) User-friendly environment; (5) Programs written on these computers were highly portable; (6) Versatile and suitable for every type of applications; (7) Require very less power to operate. Generations of Computers Disadvantages: (1) The soldering of LSI and VLSI chips on the wiring board was not an easy task and required complicated technologies to bind these chips on the wiring board; (2) The working of these computers is still dependent on the instructions given by the programmer. Generations of Computers Fifth Generation Computers • The different types of modern digital computers come under this category. • Use Ultra Large Scale Integration technology that allows almost ten million electronic components to be fabricated on one small chip. Generations of Computers Advantages: (1) Fastest and powerful computers till date; (2) Being able to execute a large number of applications at the same time and that too at a very high speed; (3) Decreasing the size of these computers to a large extent; (4)The users of these computers find it very comfortable to use them because of the several additional multimedia features; (5) They are versatile for communications and resource sharing. Classification of Computers We can classify the computers according to the following three criteria: (1) Based on operating principles (2) Based on applications (3) Based on size and capability Classification of Computers (1) Based on operating principles: Analog computers: represent data in the form of continuous electrical signals having a specific magnitude Digital computers: store and process data in the digital form. Hybrid computers: a combination of analog computer and digital computer because it encompasses the best features of both. Classification of Computers (2) Based on applications: General purpose computers: can work in all environments. Special purpose computers: can perform only a specified task. Classification of Computers (3) Based on size and capability Microcomputers: Designed to be used by individuals. Mini Computers: Can handle more data and more input and output than micro computers. Mainframe Computers: A very large computer Super Computers: The fastest type of computer that can perform complex operations at a very high speed. Computing concepts Accepting the raw data Processing the data Storing the data Delivering the output The Computer System Hardware Software Data People Computer Organisation and Architecture Computer architecture: the definition of basic attributes of hardware components and their interconnections, in order to achieve certain specified goals in terms of functions and performance. Computer organisation: the design and physical arrangement of various hardware units to work in tandem, in a orderly manner, in order to achieve the goals specified in the architecture. Central Processing Unit The main operations of the CPU include four phases: (1) Fetching instructions from the memory (2) Decoding the instructions to decide what operations to be performed (3) Executing the instructions (4) Storing the results back in the memory Central Processing Unit Registers Arithmetic Unit Logic Unit Control Unit Arithmetic Unit Arithmetic Unit is a part of the CPU that performs arithmetic operations on the data. The arithmetic operations can be addition, subtraction, multiplication or division. Logic Unit Logic Unit is a part of the CPU that performs logical operations on the data. Control Unit Control Unit is an important component of CPU that controls the flow of data and information. It maintains the sequence of operations being performed by the CPU. Main Memory Unit The main memory is referred to as the internal memory of primary memory of the computer. It is also known as Random Access Memory (RAM). Cache Memory Cache memory is a small, fast and expensive memory that stores the copies of data that needs to be accessed frequently from the main memory. Registers CPU contains a few special purpose, temporary storage units known as registers. They are high-speed memory locations used for holding instructions, data and intermediate results that are currently being processed. Internal Communications The internal communication of a processor in the computer system can be divided into two major categories: (1) Processor to memory communication (2) Processor to I/O devices communication Processor to Memory Communication The direct communication between the processor and memory of the computer system is implemented with the help of two registers: (1) Memory Address Register (2) Memory Buffer Register The reading and writing operations performed by the processor are called memory read and memory write operations. Processor to I/O Devices Communication The communication between I/O devices and processor of the computer system is implemented using an interface unit. The interface unit acts as an intermediary between the processor and the device controllers of various peripheral devices in the computer system. Machine Cycle The cycle during which a machine language instruction is executed by the processor of the computer system is known as machine cycle. Instruction Cycle Fetching: The CPU retrieves the instruction from the main memory of the computer system. Decoding: Breaking down the instruction into different parts, so that it can be easily understood before being processed by the CPU. Execution Cycle Executing: The decoded instruction is executed by the ALU of the CPU. Storing: The result computed in the execution phase is either sent to the memory or to an output device. The Bus A bus is a set of wires that is used to connect the different internal components of the computer system for the purpose of transferring data as well addresses amongst them. Data bus: used to transfer data amongst the different internal components. Modern computer systems use 32-bit data buses for data transfer. Address bus: transfers the memory addresses for read and write memory operations. Memory and Storage Systems Primary Memory: Storing the data that are being currently handled by the CPU; generally known as “memory”; Secondary Memory: Storing the results and the data for future use; generally known as “storage”; Internal Process Memory: Placed either inside the CPU or near the CPU. Memory Representation In the memory, values are represented by sequences of binary digits, know as bits. Most computers use a group of eight bits, known as a byte, to represent a character. Memory is a “bunch” of bytes or cells into which we can place data. Each cell, known as a data item, is assigned a unique number known as “address”. The CPU can identify each cell by its address. Memory Representation The byte is defined as the “smallest addressable unit” of memory. Most computers use groups of bytes, usually 2 or 4, known as “words” to represent information. Computer memories are often rated in terms of their capacity to store information. Typically, capacities are described using the unit of byte as follows: (1) 1 KB (Kilobyte)=1,024 bytes (2) 1 MB (Megabyte)=1,048,576 bytes (3) 1 GB (Gigabyte)=1,073,741,824 bytes (4) 1 TB (Terabyte)=1,099,511,627,776 bytes Random Access Memory Random Access Memory (RAM) is a volatile memory and loses all its data when the power is switched off. It is the main memory of the computer system that stores the data temporarily and allows the data to be accessed in any order. RAM can be categorised into two main types, namely, Static RAM and Dynamic RAM. Random Access Memory Static RAM: is a type of RAM in which data is stored till the power of the computer system is switched on. SRAM uses a number of transistors to store a single bit of digital information. Dynamic RAM: is the RAM in which data is stored in a storage cell, consisting of a transistor and a capacitor. The DRAM needs to be continuously refreshed with power supply because the capacitor has the tendency to get discharged. DRAM retains the data for a very short span of time, even after the power supply is switched off. Read Only Memory ROM is the memory that stores the data permanently. The data can be easily read from this type of memory but cannot be changed. ROM is most commonly used in devices such as calculators, laser printers, etc. ROM does not allow the random access of data, and allows sequential access of data. Read Only Memory ROM is divided into four types: (1) Programmable ROM: a memory chip on which the write operation of data can be performed only once. PROM is reliable and stores the data permanently without making any change in it. It is mostly used in video games and electronic dictionaries. (2) Erasable PROM: a type of ROM in which data can be erased or destroyed using Ultraviolet Light. (3) Electrically Erasable PROM: a type of ROM in which data can be erased or destroyed by exposing it to an electric charge. (4) Flash ROM: a type of EEPROM that stores the information using floating-gate transistors, which can store electric charge for a longer period of time as compared to the normal transistors. This memory is mainly used in the memory cards of mobile phones, digital cameras and ipods for storing data. Flash ROM has faster speed of reading data, as compared to any other type of ROM. Storage Systems Storage systems are the devices used for data storage. The main objective of the storage system is to permanently store data. The storage systems can be classified as follows: (1) Magnetic (2) Optical (3) Solid state (4) Magneto Optical Magnetic Storage Systems Magnetic storage systems can be defined as the storage systems that store the data on a magnetised medium, with the help of magnetised particles. Magnetic tapes, magnetic disks, hard disks, floppy disks are examples of magnetic storage systems. Can store any type of data, such as text, audio, video, image Magnetic Storage Systems Magnetic tapes: The plastic tapes with magnetic coating that are used for storing the data. They are similar to the normal recording tapes. The data stored on the magnetic tapes can be accessed using the sequential access method. Magnetic Disks: A flat disk that is covered with magnetic coating for holding information. It is used to store digital information in the form of small and magnetised needles. These needles help in encoding a single bit of information by getting polarized in one direction represented by 1, and opposite direction represented by 0. It allows the random access of data and provides the facility of erasing and rerecording the data as many times as required. Optical Storage Systems The optical storage systems use the laser light as the optical medium to retrieve as well as record data. The optical storage devices are either read-only or writable. Solid-State Storage Devices Solid-state Storage Devices were developed in 1978 by Storage Tek Company. Do not use magnetic and optical medium to store data. Instead, use the semiconductor devices. Contains all the properties of hard disk drives to store the data and use solid-state memory, which has no moving parts. The examples of SSD are flash memory cards and Universal Serial Bus (USB) devices. Storage Evaluation Criteria Access Mode: random access mode, sequential access mode, direct access mode Access Time: the time taken by the processor in completing the requests made by the user for performing the read and write operations. Storage Capacity: the size of the memory available for storing the data, and measured in terms of bytes. Storage Type: Temporary and permanent memory. Cost: the cost of the storage device used in the computer system for holding the data. Input Devices Input devices are electromechanical devices that are used to provide data to a computer for storing and further processing, if necessary. We can provide the input to a computer in two ways: (1) Manually through devices such as keyboard and mouse; (2) Directly from documents using devices such as scanners. Input Devices Depending upon the type or method of input, the input device may belong to one of the following categories: (1) Keyboard (2) Pointing devices (3) Scanning devices (4) Optical recognition devices (5) Digital camera (6) Voice recognition devices (7) Media input devices Keyboard Keyboard is the most commonly used input device. We can use a keyboard to type data and text and execute commands. A standard keyboard consists of the following groups of keys: (1) Alphanumeric keys: The alphanumeric keys include the number keys and alphabet keys. These keys are arranged in the same style as in the normal typewriters, popularly known as QWERTY layout; (2) Function keys: Arranged in a row on the top of the keyboard. Help perform specific tasks, such as searching a file or refreshing a web page; (3) Central keys: Used for controlling the movement of cursor and screen display. Include arrow keys, modifier keys such as SHIFT, ALT, CTRL; (4) Numeric keypad: Located on the right side of the keyboard. This looks like a calculator’s keypad; (5) Special purpose keys: Escape, Insert, Delete, Print Screen, Pause, Tab, Spacebar; Pointing Devices Pointing devices are the input devices that are generally used for moving the cursor to a particular location to point an object on the screen. With the help of pointing devices, we can easily select the icons, menus, windows, etc on the Graphical User Interface. Some of the commonly used pointing devices are: (1) Mouse (2) Trackball (3) Light pen (4) Joystick (5) Touchscreen Mouse A small hand-held pointing device that basically controls the two-dimensional movement of the cursor on the displayed screen. The most commonly used types of mouse are: (1) Mechanical mouse (2) Optical mouse Scanning Devices Scanning devices are the input devices that can electronically capture text and images, and convert them into computer readable form. The basic task of a scanning devices is to convert an image or the textual data into digital data, i.e., in the form of boxes, where each box represents either zero or one. The resultant matrix is known as bit map and is displayed on the screen. Scanning Devices The scanning devices can be differentiated from each other on the basis of the following characteristics: • Resolution: the closeness of the pixels in the bit • map, and vary from 72 to 600 dots per inch (dpi); Size: the small sized scanning device can scan approximately two to five inches of the document, whereas the large sized one can scan approximately up to forty inches of the document. Scanning Devices • Scanning technology: Some ones use Charged Coupled Device (CCD) arrays, whereas others use Photo Multiplier Tubes (PMT) technology. The CCD consists of a series of light receptors, which are sensitive to the variation in the light frequency. As the frequency of light changes, these scanning devices detect the change and the output obtained after scanning also gets accordingly changed. The PMT consists of a photocathode, which is a photosensitive surface used for generating the electrons. PMT is used for identifying the light emitted by the weak signals. Scanning Devices On the basis of these characteristics, the scanning devices can be categorized as follows: • Hand-held scanners: are suitable for scanning • small images rather than the whole page of text or pictures, and are generally used for identifying the bar-code label of the products. Flat-bed scanners: consist of a flat surface composing of glass pane on which the documents are kept for scanning. Under this glass pane, there is xenon light and a CCD, which consists of an array of red, green and blue filters. Scanning Devices Drum scanners: consist of a large drum, which is used for scanning the documents. These scanners make use of the PMT technology, instead of the CCD technology. The resolution image of these scanners is very high, ranges form 8000 dpi to 11000 dpi. Slide scanners: are used for scanning slides as well as film negatives. These scanners are also known as film scanners as they can easily scan the original image of the film. The dark areas appear light and the light areas appear dark. Optical Recognition Devices Optical recognition devices are used for recognising the characters optically. The optical recognition devices basically make use of optical scanner for inputting data. Unlike keyboards, the optical recognition devices do not enter the data by pressing the keys. They help the users in saving a lot of time. Commonly used optical recognition devices are: Optical Character Recognition (OCR) devices: scan a particular document by recognizing its individual characters and converting it into the editable form. Optical Recognition Devices • Optical Mark Recognition (OMR) devices: help in obtaining the data from the marked fields. These devices prove to be of great use in recognizing characters in question sheets, enrolment forms, registration forms, employee payroll, etc. Most popularly, the OMR devices are used for scanning the documents having multiple choices as in the question papers used in schools, colleges, etc. Optical Recognition Devices • Magnetic Ink Character Recognition (MICR) devices: special devices used for recognizing the characters written with magnetic ink consisting of iron oxide particles. These devices were specially developed for the banking operations. The details on the bank cheques, such as cheque number, bank and branch code are written with the magnetic. Digital Camera A digital camera is a handheld electronic device that is used to capture the image of an object electronically. The digital camera consists of a built-in computer, which helps in recording the images electronically. The following are the main features of the digital camera: • Capturing and storing thousands of images on a • • • single memory chip Editing as well as deleting the images Recording the video clip with sound Showing the just recorded video clip on the camera screen Digital Camera The image captured by a digital camera is in the digital format and can be easily downloaded on a computer system. The quality of the pictures captured by a digital camera depends on the resolution factor. The more the resolution of a digital camera, the better is the image quality. Voice Recognition System The voice recognition devices generally record the voice of a person and transform it into electrical signals. The electrical signals are then converted into the machine readable code. The voice recognition system only recognises the voice of the speaking person rather than what he speaks. The voice recognition devices are used for various purposes such as dictation, training air-traffic controllers, etc. These systems allow users to communicate with computers directly without using a keyboard or mouse. Data Acquisition Sensors Sensors are the devices that are used for detecting and measuring the physical quantities, such as heat, temperature, and converting them into electrical signals. The sensors are most commonly used in data acquisition systems. The data acquisition system collects the electrical signals from various devices and converts them into the digital signals for further assessment. Media Input Devices The input devices, which are generally used in media for communicating with the mass audiences, are known as media input devices. The following are the most popularly used media input devices: • Microphone • Webcam • Graphics tablet Output Devices • • • • • Output devices receive the processed data (information) from the CPU and present it to the user in a desired form. They act as an interface between the computer and the user. The main task of an output device is to convert the machine readable information into human-readable from which may be in the form of text, graphics, audio or video. Depending upon the form of output required, the output device may belong to one of the following categories: Display monitors Printers Plotters Voice output systems Projectors Output Devices While the printers and plotters provide the physical form of output known as hard copy, the display monitors, voice output systems and projectors provide temporary output known as soft copy. Unlike hard copy, soft copy is not a permanent form of output. Display Monitors Earlier the display monitors were capable of displaying the characters only in a single font and in a single color. These characters were arranged in a rectangular grid on the screen. The display screens, which are available today, support many fonts and colors. Different types of display monitors use different technology for displaying the data. Display Monitors Cathode Ray Tube (CRT) Monitor: contain an empty glass tube with a phosphor coated fluorescent screen and a source of electrons known as electron gun. A CRT monitor has many advantages, such as a high contrast ratio and color depth. It also provides a change in the resolution without affecting the clarity of the picture. But it is very bulky and occupies a lot of space on the desk. It also consumes a lot of power and produces a large amount heat. Display Monitors Liquid Crystal Display (LCD) Monitor: Use liquid crystals technology to display the images. An LCD monitor is small in size and light in weight so it occupies less space on the desk. Also, the power consumption by an LCD monitor is very less. However, it has a weak color quality as compared to a CRT monitor. Thin Film Transistor (TFT) Monitor: A TFT monitor is similar to an LCD monitor except for one difference that it uses thin film transistor technology along with liquid crystal technology to improve the quality of the image. Printers A printer is a computer hardware that generates the hard copy of the information processed by a computer system. • Impact Printers: there exists a mechanical contact • between print head and paper. Print head is the part of the printer that resembles a hammer and is responsible for transferring the ink to the paper in the form of required characters. Impact printer contains an individual print head for each character. Non-Impact Printers: there exists no mechanical contact between the print head and paper. These printers spray ink on the paper with the help of a nozzle. The most popular ones are ink-jet printers and laser printers. Plotters Plotter is a device used to print high quality graphics and images. It uses one or more pens to produce a high quality drawing. These pens change their positions and draw continuous lines to produce an image. The plotters were used as a substitute to the colored printers when the printers were very expensive and were also not capable of drawing bigger images such as graphs. Voice Output Systems Voice output systems record the simple messages in human speech form and then combine all these simple messages to form a single message. The voice response system is of two types: (1) a reproduction of human voice and other sounds; (2) speech synthesis. The basic application of a voice output system is in Interactive Voice Response systems, which are used by the customer care or customer support departments of an organization, such as telecommunication companies, etc. Projectors A projector is a device that is connected to a computer or a video device for projecting an image from the computer or video device onto the big white screen. A projector consists of an optic system, a light source and displays, which contain the original images. Projects were initially used for showing films but now they are used on a large scale for displaying presentations in various situations.