4.5.5 FoDR (Information coding systems) Flashcards
(15 cards)
What is ASCII?
a character encoding system that uses 7 bits to represent 128 characters, including English letters, digits, and some control characters.
What is Unicode?
Unicode is a universal character encoding system that uses up to 32 bits to represent over 1.1 million characters from nearly all written languages and symbol sets.
Why was Unicode introduced?
to allow consistent encoding of characters from all languages, overcoming tHohe limitations of ASCII which could only represent English characters.
How is Unicode better than ASCII?
Unicode can represent a much wider range of characters, making it suitable for global communication and multilingual software.
How does parity bit checking work
An extra bit is added to make the total number of 1s either even (even parity) or odd (odd parity).
The receiver checks the number of 1s to see if a single-bit error occurred.
What are the drwabacks for parity bit checking
Parity can detect if an error has happened but cannot locate the error or detect multiple errors reliably.
How does majority voting work, and give an example
Each bit is repeated an odd number of times (usually three) before transmission. The receiver selects the most frequent value as the correct bit.
For example, if “110” is sent as “111 111 000”, the receiver will choose “110” because it appears most frequently.
What are the drawbacks of Majority Voting
- it cannot detect multiple errors reliably
- it increases the volume of data transmitted, which slows down transmission.
How do checksums work
A checksum is added to data to detect errors during transmission.
It’s generated by applying an algorithm (checksum function) to the data block, producing a value that is transmitted with the data.
The receiver recalculates the checksum and compares it with the transmitted value. If they don’t match, an error is detected.
What are the 2 main checksum methods
Longitudinal Parity Check (XOR method)
Sum Complement (Binary Addition method)
Explain how longitudinal parity check works
The data is divided into sets, and the XOR of each set is calculated.
The result is appended as the checksum.
The receiver XORs the received data and checksum. If the result is 0, the data is correct; if 1, there’s an error.
Explain how Sum complement check works
The sets of bits are added as unsigned binary numbers
The checksum is the two’s complement of the result.
The receiver adds the data and checksum and checks if the result is 0.
If there’s a 1 in the result, it indicates an error.
What are the disadvantages of the Checksum error checks
- cannot identify which bit is corrupted
- Errors in multiple bits within the same set goes undetected
How does check digit checking work
Check digits are calculated using algorithms The check digit is derived from the other digits in the number. When entered, the system recalculates the check digit and compares it to the original. If they don’t match, an error has occurred.
What are the disadvantages of check digits
- Cannot identify which digit is incorrect
- Multiple errors can go undetected
