Information literacy Knowing how to find data from several sources， select relevant material， analyse and organise it into a form that can be used to make Computers have become the tools people use to access and manage Information technologists are people who analyse and design the What is a computer? Tradition definitions of computers include • A machine that accepts data and processes it into use • A computer is a binary， digital， electronic， stored program • While a computer is commonly a digital machine， analogue machine do An electronic device， operating under the control of instructions stored in its own memory unit， that can accept data (input)， process data arithmetically and logically， produce results (output) from the processing and stores results for future Many computers receive and send data (communicate) across networks LAN and W A computer system consists of hardware and What is hardware? Hardware Hardware is physical devices or components that can be physically handled – you can thou Input Devices Input devices convert data that humans collect into coded electrical signals that a computer can The central processing unit The electronic processing takes place in the CPU The CPU consists of • A control unit that controls all of the computer’s functions and an • Arithmetic and logical unit (ALU) that performs any calculation Memory Memory holds all programs and What is RAM currently open? Data (notes) Word processor OS Output devices Output devices convert the computer’s electronic signals back into information Secondary storage devices These devices store programs and data The programs and data are not necessarily (or likely to be) in current E DVD CD Communication devices These devices enable a computer to connect to another List the six different type of hardware? Secondary storage(external)， input， processor， output ， memory， C Name eight pieces of hardware USB， keyboard， monitor， screen， RAM， ROM， VDU， M The system unit and peripheral devices The system unit is the computer Peripheral devices are any devices around the outside， or in other words， plugged into the (back of) the Peripheral devices include the key board， mouse， printer， joy stick and Peripheral devices are any devices around the outside， or in other words， plugged into the (back of) the Peripheral devices include the keyboard， mouse， printer， joy stick and What else does a computer have? Software Software is a computer program ，which is a detailed set of instructions that directs a computer to perform the tasks necessary to process data into These instructions are written in languages that computer can Software includes computer games， a word processing packing， an accounting package， amongst Definition of a computer system • A computer system is the configuration of hardware and software， functioning together， to process data into useful information， in order to achieve a purpose for a human What is data? • Data is raw facts， be they numbers， words， images and sounds， that can be input into a Mary a name is a piece of data What is information? • Information is processed data， that has meaning and is John is a list of names who scored an A grade on an exam John A Chai A Pam A Commodore $23 500 Magna $21 500 Falcon $19 800 The system unit contains the • Motherboard • CPU • Memory • Other electronics It is where the computer program instructions are executed and the data is manipulatedThe Processor CPU The CPU interprets and carries out basic instructions that operate the computer， the CPU contain the • Control unit and the • Arithmetic logic unit Control unit The control unit directs and coordinates the computer’s For every single instruction， the control unit repeats four basic operations， • Fetching • Decoding • Executing • Storing CPU speed The CPU’s speed may be measured in MIPS The number of millions of instructions per second Arithmetic/logic unit The ALU performs all calculations， which involve • Arithmetic operations 2+3 • Comparison operations age>=17 • Logical operations pass Processing instructions A CPU may begin executing a second machine cycle before completing the first-referred to as Current CPU’s can pipeline up to 4 Storage within the CPU Registers temporarily hold data and The computer’s clock A System clock is necessary to control the timing of all computer Each tick of the clock is referred to as a clock Clock speed is the speed at which a processor executes A hertz is one cycle per second and a megahertz is 1024 by1024 and a gigahertz is 1024 by 1024 Memory Memory is the temporary storage place for data and (program) Memory is measured in • Kilobytes 1024 bytes 2^10 • Megabytes 1024* 1024 bytes 2^20 • Gigabytes 1024*1024*1024 bytes 2^30 Representation of data Digital computers are built from many small electronic Each circuit， at any point of time can be turned OFF or ON Hence these devices are called two state Binary Digit 0and 1 Each off or on digital value is called a bit， short for binary A 1 bit computer would be able to distinguish between two values-characters， symbols or Hardly sufficient for the characters on the keyboard Bits Characters 1 2 2 4 3 8 4 16 5 32 6 64 7 128 8 256
PrefaceThe ARPANET – the Department of Defense network that is the ancestor of today’s Internet—was built in the late sixties using a proprietary protocol This first protocol proved to have shortcomings for linking with other networks， which led to the development of Transfer Control Protocol/Internet Protocol (TCP/IP) TCP/IP used 32-bit address These soon proved to be unwieldy for most users， even when expressed in the less daunting formant of four 8-bit decimal numbers， delimited by The obvious solution was a scheme for addressing computers by After all， people relate much better to names and find it much easier to remember the computer in the corner as “Frodo，” rather than “”The First Generation: Hot TablesThe desire to refer to machines by name instead of number led to the first IP address management scheme: the host The host table is a file that contains all the IP address in use on a network， along with their The host table provides a mapping from a host’s name to its IP address， as well as reverse mapping: Given a host’s IP address， the user can look up its For a host table to be most user useful， it must contain the names of all the hosts with which a given host might want to For the ARPANET， that mean that the host table had to contain the names and IP address of every host on the Such a file was maintained by the Network Information Center (NIC)， the central organization responsible for managing the ARPANET The file was called HOSTSTXT and was similar in format to the/etc/hosts file on UNIX Network administrators all over the network e-mailed host table changed to the NIC every time they added or deleted a host or changed a host’s IP The NIC made the changes to its master host table， which it made available via File Transfer Protocol (FTP) Administrators periodically downloaded the latest version of the host table to stay
