1. Networks & I/O Devices

2. 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.

3. 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

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

5. 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

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

7. 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

8. 101011100 Binary 348 Number (base 10) Divide by 2 Odd or Even 174 87 1
174 87 1 43 21 10 5 2

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

10. 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 and respectively

11. 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.

12. 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

13. 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)

14. ASCII Hex Code

15. 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