GCSE Computing/Computing hardware/Introduction to Binary Logic/Binary logic/Bits Bytes Nibbles

What you need to know
Define the terms bit, nibble, byte

A bit
If we only have one wire (or other piece of data storage), it can be on or off. So we could only store a very small piece of information, such as if one thing were true (on) or false (off). This is called a bit.

A nibble
Usually we want to store more than true or false. It could be anything, but let's start simply with trying to store a moderate size number. If we had four bits together we could store 16 numbers (0 to 15).

Exercise
Check that you understand why four bits lets you store 16 different numbers, by writing out every possibility. The start and end of the table to do it is here:

A byte
A nibble isn't a very useful amount. The main size up from a bit that people usually talk about is a byte, which is normally made up of 8 bits. If we had eight bits we could store 256 numbers (0 to 255).

Exercise
Check that you understand why eight bits lets you store 256 different numbers, by writing out the first ten numbers (0 to 9) and the last ten numbers (246 to 255).

ASCII Table
Let's look at trying to store a single letter. It's not as simple as 26 letters - we might need capitals or lower case, plus there are punctuation marks etc. The table below shows some of the characters available. If you look at the column headed Glyph it shows what letter or symbol it is. The Binary column tells you the binary equivalent. Again, think why we care about binary. A capital letter A, which has the binary 1000001 (65 in Base 10) means that, if this is being transmitted round a computer wires 1 and 7 have a voltage and the others don't.

ASCII - more detail
You may wonder why the table above starts at 32 and not 0. The answer is that codes 0 to 31 are used for other things that aren't letters, such as a backspace or a new line character.