Character Coding Schemes

ASCII
- Uses 7 bits so can therefore represent 128 different characters.
- A different binary number is assigned to each character.
Example- The letter A has a binary number assigned to it - 1000001
- Some of the characters are control codes, such as tab.
- The 8th bit is used usually for error checking.
- Extended ASCII uses the 8th bit in a byte to code more than characters, such as symbols like copyright and characters in french.
- Digits have different binary representations when they are stored as text rather than numbers.

Unicode
- Unicode represents characters using 16 bits instead of 8.
- Unicode provides a unique number for every character no matter what program or language.
- Extended ASCII is included in Unicode.
Example- The letter A is coded as 0000000001000001 in binary
                                                                            0041 in Unicode
                                                                                65 in denary

Error Checking and Correction
- Single Parity Bit - Is an extra bit.
                           - It is added to the pattern for error checking
                           - A computer system uses either a ODD bit parity or an EVEN bit parity
                           - In an odd bit parity the number of 1 bits are odd
                           - In an even bit parity the number of 1 bits are even
Example: Odd
  11001100
111001100
Example: Even
  110001000
1110001000

- If an ASCII character is transmitted using an even parity the reciever will check the parity after it has been transmitted.
- If the parity is odd then there has been an error in the transmission.