Definition. Introduction to Computers. Computer System. Computer System. Hardware. Hardware

Transcription

1 Introduction to Computers Seeram Chapter 2 Definition Computer = a machine for solving problems Technical definition = a high-speed electronic computational machine that accepts information in the form of data and instructions through some input device and processes this information with arithmetic and logic operations from a program stored in its memory. Computer System 3 Main Components Hardware Software Computer user Computer System Hardware physical components of the machine Software instructions that make the hardware work to solve problems Users design hardware, software and operate the computer systems Hardware Input device Central processing unit (CPU) Internal memory Output device External memory or storage Hardware Input hardware devices such as keyboard Processing hardware CPU and internal memory CPU is the brain; a control unit that controls the activities of the computer and an arithmetic logic unit (ALU) which performs mathematical calculations and data comparisons Main memory permanent storage for programs that make the computer run 1

2 Hardware Output printer, monitor External storage mag tape, disks, cd-rom Software Hardware receives its instructions from the software Sets of instructions are called programs 3 categories of software System software start up computer and coordinates activities of hardware Applications software program used to solve specific problems Software development tools BASIC, FORTRAN, C++ Historical Perspectives First generation computers ( ) vacuum tubes and punch cards Large, slow and produced lots of heat Second generation computers ( ) solid state devices (transistors) Smaller, less heat, and required less power to operate Historical Perspectives Third generation ( ) Silicon chips Smaller, greater speed and increased reliability. Multi-processing, and more applications software Fourth generation ( ) large-scale integration; thousands of circuits were set on one chip. Microprocessor Historical Perspectives Fifth generation (1987 present) gallium arsenide based circuitry. Parallel processing and extremely fast processing speeds. 2

3 Classifications Supercomputers CRAY-2 large, highcapacity computers. Can process data at extremely high speeds. Used in research, scientific modeling, weather forecasts, and oil exploration Mainframe large, high-level computers capable of rigorous computations. Large memory and can support many pieces of peripheral equipment. Used at banks, universities, large business, and government Classifications Minicomputer mid level computer built to perform complex computations while dealing efficiently with a high level of input and output from a variety of users. Often connected in a network Microcomputers PC, currently as powerful as mainframes of a few years ago. Computer Architecture Refers to the structure of a computer and includes hardware and software. Specifically refers to the computer systems, computer chips, circuitry, and systems software Types of Architecture Complex instruction set computing (CICS) has many built in operations Includes mainframes, and microcomputers Reduced instruction set computing (RISC) high level machines, SUN, IBM 6000, Motorola RISC is faster if memory is fast so that no time is wasted fetching instructions CISC is faster if memory is slow because the same work can be done without fetching as many instruction codes Terminology Serial or sequential processing simple form of processing data one instruction at a time Distributed processing information is processed by several computers on a network. Separate computers that perform different tasks Terminology Multitasking computer works on more than one task at a time Multiprocessing uses two or more connected processing units. Each processor works on a different set of instructions. This provides increased speed. 3

4 Terminology Parallel processing two or more processors running simultaneously. A number of processes can be carried out at the same time Pipelining method of fetching and decoding instructions. Several program instructions are in various stages of being fetched or decoded. Speeds execution time Terminology Binary Digit (bit) = a single binary number Because binary digits can be long they are often combined into groups called bytes. Memory capacity is measured in bytes 1 thousand bytes = 1 kilobyte 1 million bytes = 1 megabyte 1 billion bytes = 1 gigabyte Binary coding schemes People enter information into computers in the form of characters. The characters must be represented in binary code so that the computer can understand. Two types of conversion schemes exist Extended binary coded decimal interchange (EBCDID) IBM Mini and Mainframes American standard code for information exchange (ASCII) microcomputers Computer Hardware Input hardware Keyboard Dumb terminals Smart terminals Intelligent terminals Non-Keyboard Light pen Mouse Touch screen Processing Hardware Speed and power are two terms often used to define hardware Speed how fast the computer processes data Power speed + other characteristics: storage capacity and memory size Processing Hardware Processing Hardware (CPU) Control unit directs activities of the computer through programs stored in memory. Directs the flow of data throughout the computer Arithmetic-logic unit (ALU) executes arithmetic and logic operation including addition, subtraction, multiplication, division, and comparisons 4

5 Processing Hardware Register temporary storage where information is either discarded or sent to internal memory Bus or Bus Line provides a path for the flow of electrical signals between units. The amount of data transported at a single moment is called the bus width. A computer with a large bus size will be faster Processing Hardware Memory called primary storage or internal memory. Stores the information entered in the computer for processing. Stores the program that provides the instructions for processing the input information Stores the results of the processing Processing Hardware Internal Memory Types Rom read only memory PROM EPROM EEPROM Ram random access memory Storage capacity expressed in megabytes Hard copy Printers Plotters Camera output Soft copy CRT Output Hardware Mag Tapes Disks Storage Hardware Optical Disks Laser beam writes data on the surface of a disk by burning tiny pits onto the disk surface. Later a lower intensity laser is used to scan the pits. This information is interpreted by a photo detector which measures the geometry and distribution of the pits 5

6 Optical Disks 3 types CD-ROM read only WORM Write once read many Erasable Optical Disk Made of gadolinium, terbium, or iron a laser beam heats a small region of magnetized ferromagnetic film and causes it to lose its magnetization. The region becomes magnetized in the opposite direction during cooling and in the presence of a magnetic field. Computer Software Programming Languages Machine Assembly Procedural Problem oriented Natural Computer Software Applications Software Programs developed to perform specific tasks Systems Software Operating System controls the allocation and usage of computer hardware resources such as memory, central processing unit, disk space, and peripheral devices System software includes at least four types of programs Boot strap loader Diagnostic routines Input/output system programs Software Interfacing Command Driven The user types in a variety of learned commands to initiate the operations of the system i.e. dir Menu-driven user selects commands from a menu of options Graphic user interface a large variety of icons and menus Originally developed by Xerox (at Palo Alto) and initially used by Apple to develop the Macintosh. Later became available for IBM type computers as Window Network Topologies Four main types Bus Star Ring Hierarchical Bus Network Devices are connected so that each device is responsible for its own communications control. There is no host computer or file server 6

7 Star Network Characterized by a host computer or file server to which several computers are connected. Ring Network The devices (mostly mainframes) are connected to form a ring without a host computer or file server Hierarchical Network Consists of a central host computer to which other computers are connected. These computers then serve as hosts to several smaller machines. Typically a mainframe plays host to several minicomputers which play host to several microcomputers Network Connectivity Local area network (LAN) Computers and hardware located in the same building Metropolitan area network (MAN) Several LANs in separate buildings across a city Network Connectivity Wide are network LANs are connected to MANs are connected all across the country or world = WAN Use Bitnet and Internet to send and share data The Internet Larges computer network in existence Created by the US Department of Defense to ward off attacks against one main computing building. Software was created which allowed information to be broken down and then reassembled Software is referred to as transmission control protocol/internet protocol (TCP/IP) 7

8 The Internet TCP Manages packets of information and their re-assembly IP Ensures that the packets arrive at their appropriate remote computers The Internet 1990 Dr. Berners-Lee developed the world wide web (www) to facilitate communications with remote computers through a set of links. The name web refers to his vision of these links as a spiders web Dr. Berners-Lee goal was to communicate more easily with his colleagues by linking with their computers. Major Components of the Internet User must first access a server computer called the internet service provider The server relays the user s message to the internet and the internet returns or requested information from the server Web Browser Allows users to use a mouse to point and click on text, drawings, and pictures. Internet Components Web sites can be located with a uniform resource locator (URL) that must conform to a specific format to ensure successful communications. Parts of the URL http protocol for communication links (hypertext transfer protocol The ISP address or domain name and the final portion of the domain name, or top-level domain, which demonstrates the type and f h Internet Components The URL ends with path, directory and file name Computers in Radiology Picture Archiving and Communications System (PACS) main components Image acquisition imaging modalities Storage and Retrieval from an optical jukebox or tape storage system Display and output images can be displayed on workstations Communication and networking PACS/RIS interfacing integration with radiology information systems 8