Networks & I/O Devices

Networks & I/O Devices Computer and communication systems are essential because of the way in which software and hardware process data into information and then transfer this data/information to other locations. Students will develop an understanding of Networks & I/O Devices concepts that underpin computer devices and how these concepts apply to networks.

Networks & I/O Devices Typical view of a Personal computer includes the central box, a display monitor, printer, keyboard and mouse. This is the user’s view. However we need to view the PC in regards to the functionality of its components. Every computer is composed of 5 major blocks: Central processor – does the actual computing Memory devices –storage of information Input devices – get info into the computer Output devices – get info out of computer Communication devices – allow computers to communicate with each other

Electrical view of inside a computer Input Devices Communications Output Devices Interconnecting wires Central Processor Memory Devices

Networks & I/O Devices Currently you have been using decimal numbers to represent values – we call this base 10 (0 – 9) However electronic circuits have just two states - on and off which are represented by base 2 or binary (0 – 1) A binary number is composed of a sequence of n bits There are 8bits in a byte A kilobyte or kb will have 1024bytes

Binary Numbers Proceeding from right to left the successive bits have weights of Ex. The number 13 (base 10) is represented by 1101 (base 2)

Binary Numbers We can convert a number from decimal to binary by repeatedly dividing it by two until the quotient is zero, keeping track of the remainder at each step. To convert 348 (base 10) to binary

101011100 Binary 348 Number (base 10) Divide by 2 Odd or Even 174 87 1 174 87 1 43 21 10 5 2 101011100

Binary Numbers As there are 8 bits in a byte we can represent numbers from 0 (0000 base 2) up to 255 (11111111 base 2) or 256 actual numbers or integers Larger numbers are coded as Word i.e. #400 would require 2 bytes or 16 bits - 110010000(base 2) Note the preceeding bits are left off as they are just zeros

Binary Numbers We need to represent negative numbers in base 2. We either use sign and magnitude or 2’s complement Sign and Magnitude Negative numbers in base 2 are represented by the left most bit being a 1 i.e. +10 and -10 in 8-bit are represented by 00001010 and 10001010 respectively

Binary Numbers As this becomes tedious and prone to errors, large binary numbers contain many digits and are hard to remember. For this reason binary numbers are often represented in hexadecimal (base 16) notation, often called hex. A number that requires 32 bits for its representation can be represented using only 8 hex digits.

Binary Numbers Hence only 16 symbols are required to represent a hex digit – numbers 0-9 and the letters A to F The number 3FC (base 16) represents the value

Natural Numbers We know that the set of numbers is infinite however a computer is forced to assume the set of numbers is finite, and therefore there is a largest number. i.e. using a byte or 8 bits we can represent any unsigned number between 0 and 255 Other data units used are Half word (0-65,535), Word (~4 billion) and Double word (0- 16,000,000,000,000,000,000)

ASCII Hex Code

Character Strings We store the length of a string in the first byte allocated to it followed by the sequence of characters Length/character representation of a string Length H e l o 05 48 65 6C 6F