1. Networks & I/O Devices
July 10, 2019

2. 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
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3. 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
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4. 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

5. 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

6. 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

7. Data Communications
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8. Data Communications Data is the raw material – i.e. before processing
Information is the organized data – after processing
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9. 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

10. 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

11. 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

12. 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

13. 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

14. 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 to 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

15. 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.'
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16. 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
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17. 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