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Lesson 16 - Units
2
The seven bit number:
1
1101011
Units
Parity bits
Has 5 1's so will have to have a 1 parity bit added to even out the number of 1's
1111000
0
✳✱*
already has an even number of 1's, so the parity bit will be set as 0
Because each bit can be one of two values, we can use a formula to work out the number of unique combinations of 1's and 0's for groups of binary bits put together
Used to check for errors
E.G. 4 bit numbers have 2 to the power of 4 (16) possible combinations
If the computer reads one bit incorrectly the error will be picked up as the number of 1's will no longer be even!
This falls down if two bits are read incorrectly as the error won't be picked up!
A digit added to the end of a number to check if the previous numbers are correct
Task
Parity bits are either odd or even
An odd check digit would seek to highlight the error doing the opposite, by ensuring that a 'normal' byte of information should have an odd number of 1's
They are used to make sure that the number of 1 bits is either odd or even
Units
Binary is represented in a computer by the presence of absence of electricity
EVERYTHING a computer processes must first be converted to binary
Each 1 or 0 is a bit (Binary Digit) - A number of 11011 is therefore 5 bits in size
Lesson Objectives
To know the different units of measurements used in CS
To understand the relationship between units and binary
To understand how parity bits are used to check for errors.
Revise, Recap, Review
3 features of an IDE
2 registers found within a CPU
1 pseudocode for a program that prints out the 2 times table up to 2 * 10
Lesson 16 - Units
Units
When we measure anything we always give a unit - CM, MPH, MPG, Stones and LBS etc.....
When we measure the size of files on a computer we also use units!
Task
Create flashcards explaining how odd and even parity bits may be used to check for errors
1024/1000
We generally refer to a GB as being 1000 MB, but that isn't strictly true....
2 to the power of 10 is actually 1024, so a GB is really 1024 MB
Either answers will be accepted in your exam