Networks & I/O Devices July 10, 2019

Data Communications There are several forms of sharing information across communication channels Broadcasting (1 to many) Networking (1 to 1) The purpose of a data communications system is to exchange information or data between two agents July 10, 2019

Data Communications Claude Shannon composed a general model for data communications in 1946 which is at once both simple and fundamental, composed of six components July 10, 2019

Data Communications Brain Vocal cords Air Students talking Ear You An information source generates a message A transmitter encodes the message as a signal The signal is transmitted over a communication channel A source of noise is usually present in the communication channel that can impact in unknown ways on the encoded signal The receiver extracts a signal from the communications channel and converts it back into the form of a message The destination receives the message Brain Vocal cords Air Students talking Ear You July 10, 2019

Data Communications Computers process digital data Data is information represented by a digital symbol system (ASCII code) All forms of information must be converted to a digital form for processing The process of converting information to a binary form is called digitization July 10, 2019

Data Communications Messages in computer network communication systems are encoded as a stream of binary numbers (0’s and 1’s) The signal is transmitted as some type of electromagnetic energy (electrical, optical or radio waves) July 10, 2019

Data Communications July 10, 2019

Data Communications Data is the raw material – i.e. before processing Information is the organized data – after processing July 10, 2019

Files The File A group of related records A collection of related data The primary unit of data storage May contain program instructions May contain data July 10, 2019

Files Types of files Files that are unique to the operating system ex. COMMAND.COM in DOS (MS-DOS short for Microsoft Disk Operating System) Files that are shared i.e. Printer drivers used by both the OS and applications Files with data only i.e. A word processing doc July 10, 2019

Files Directory - a list of file names stored on a disk or a portion of a disk Root directory – primary directory; every disk has one Subdirectories Located under the root directory Used for file organization July 10, 2019

Files File formats indicated by a series of patterns, standards and codes identify the unique data stored in the file by the application that created it .jpg is a graphic file, .exe is an executable or program file July 10, 2019

ASCII ASCII (American Standard Code for Information Interchange). To most of us, ASCII is nothing more than a set of characters that any text based application or game can use in order to present contents to the users of these programs. ASCII was a communication standard as well as a character display standard because before that, no two brand of computers could talk to each other. But to understand the depth of all this, you have to put yourself all the way back to 1963, when it all really began. July 10, 2019

ASCII Back in the early 1960s there was no ASCII standard. Hence computer manufacturers were doing things pretty much any way they saw fit. This resulted in the following situation: Different computers had no way of communicating with each other. Each manufacturer had their own way of representing the letters of the alphabet, numbers and the likes. There were over 60 different ways, at the time, to represent these letters, numbers and any specific symbols. I.B.M. with it's different equipment had nine different character sets. Bob Bemer worked for I.B.M. (International Business Machine) from 1956 to 1962. Bob Bemer played an important role in the establishment of the ASCII standard and got coined the Father of ASCII. The work towards an ASCII standard started back in 1960. July 10, 2019

ASCII Today ASCII is still being used except for Windows machines which now use Unicode as their new standard. Unicode was developed in 1981; ‘The original purpose of the Unicode Consortium was to 'standardize, extend and promote the Unicode character encoding, a fixed-width, 16-bit character encoding for over 60,000 graphic characters.' July 10, 2019

Data Representation Using binary digits we can represent a piece of information that has two possible values False or true Off or on Closed or open Male or female Encode one value with 0, the other with 1 July 10, 2019

Data Representation However what if there are more than two values? We can use a collection of bits 2 bits to encode up to four values (00 01,10,11) 3 bits to encode up to 8 values N bits to encode up to 2^n values Example: colours 000 (black) 001(red) 010(green) 011(yellow) etc (these are hard coded into the program instructions) July 10, 2019