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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:

Figure 1 - Table for a nibble
Eights	Fours	Twos	Ones	Equals
0	0	0	0	0
0	0	0	1	1
0	0	1	0	2
...	...	...	...	...
1	1	1	1	15

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.

Binary	Oct	Dec	Hex	Glyph
010 0000	040	32	20	␠
010 0001	041	33	21	!
010 0010	042	34	22	"
010 0011	043	35	23	#
010 0100	044	36	24	$
010 0101	045	37	25	%
010 0110	046	38	26	&
010 0111	047	39	27	'
010 1000	050	40	28	(
010 1001	051	41	29	)
010 1010	052	42	2A	*
010 1011	053	43	2B	+
010 1100	054	44	2C	,
010 1101	055	45	2D	-
010 1110	056	46	2E	.
010 1111	057	47	2F	/
011 0000	060	48	30	0
011 0001	061	49	31	1
011 0010	062	50	32	2
011 0011	063	51	33	3
011 0100	064	52	34	4
011 0101	065	53	35	5
011 0110	066	54	36	6
011 0111	067	55	37	7
011 1000	070	56	38	8
011 1001	071	57	39	9
011 1010	072	58	3A	:
011 1011	073	59	3B	;
011 1100	074	60	3C	<
011 1101	075	61	3D	=
011 1110	076	62	3E	>
011 1111	077	63	3F	?

Binary	Oct	Dec	Hex	Glyph
100 0000	100	64	40	@
100 0001	101	65	41	A
100 0010	102	66	42	B
100 0011	103	67	43	C
100 0100	104	68	44	D
100 0101	105	69	45	E
100 0110	106	70	46	F
100 0111	107	71	47	G
100 1000	110	72	48	H
100 1001	111	73	49	I
100 1010	112	74	4A	J
100 1011	113	75	4B	K
100 1100	114	76	4C	L
100 1101	115	77	4D	M
100 1110	116	78	4E	N
100 1111	117	79	4F	O
101 0000	120	80	50	P
101 0001	121	81	51	Q
101 0010	122	82	52	R
101 0011	123	83	53	S
101 0100	124	84	54	T
101 0101	125	85	55	U
101 0110	126	86	56	V
101 0111	127	87	57	W
101 1000	130	88	58	X
101 1001	131	89	59	Y
101 1010	132	90	5A	Z
101 1011	133	91	5B	[
101 1100	134	92	5C	\
101 1101	135	93	5D	]
101 1110	136	94	5E	^
101 1111	137	95	5F	_

Binary	Oct	Dec	Hex	Glyph
110 0000	140	96	60	`
110 0001	141	97	61	a
110 0010	142	98	62	b
110 0011	143	99	63	c
110 0100	144	100	64	d
110 0101	145	101	65	e
110 0110	146	102	66	f
110 0111	147	103	67	g
110 1000	150	104	68	h
110 1001	151	105	69	i
110 1010	152	106	6A	j
110 1011	153	107	6B	k
110 1100	154	108	6C	l
110 1101	155	109	6D	m
110 1110	156	110	6E	n
110 1111	157	111	6F	o
111 0000	160	112	70	p
111 0001	161	113	71	q
111 0010	162	114	72	r
111 0011	163	115	73	s
111 0100	164	116	74	t
111 0101	165	117	75	u
111 0110	166	118	76	v
111 0111	167	119	77	w
111 1000	170	120	78	x
111 1001	171	121	79	y
111 1010	172	122	7A	z
111 1011	173	123	7B	{
111 1100	174	124	7C	\|
111 1101	175	125	7D	}
111 1110	176	126	7E	~

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.

Wikipedia has related information at ASCII

Category:Book:GCSE Computing#Computing%20hardware/Introduction%20to%20Binary%20Logic/Binary%20logic/Bits%20Bytes%20Nibbles%20

Wikimore

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

What you need to know

A bit

A nibble

Exercise

A byte

Exercise

ASCII Table

ASCII - more detail