Hexadecimal

Hexadecimal (base 16) writes the values 0-15 as single digits: 0-9, then a-f. Can you spot the relationship between binary (base 2), octal (base 8) and hexadecimal (base 16)?

Binary	Octal	Decimal	Hexadecimal	Base64
0	0	0	0	A
1	1	1	1	B
10	2	2	2	C
11	3	3	3	D
100	4	4	4	E
101	5	5	5	F
110	6	6	6	G
111	7	7	7	H
1000	10	8	8	I
1001	11	9	9	J
1010	12	10	A	K
1011	13	11	B	L
1100	14	12	C	M
1101	15	13	D	N
1110	16	14	E	O
1111	17	15	F	P
10000	20	16	10	Q
10001	21	17	11	R
10010	22	18	12	S
10011	23	19	13	T
10100	24	20	14	U
10101	25	21	15	V
10110	26	22	16	W
10111	27	23	17	X
11000	30	24	18	Y
11001	31	25	19	Z
11010	32	26	1A	a
11011	33	27	1B	b
11100	34	28	1C	c
11101	35	29	1D	d
11110	36	30	1E	e
11111	37	31	1F	f
100000	40	32	20	g
…	…	…	…	…

One hexadecimal digit is 4 bits, so 2 digits = 8 bits = 1 byte. That makes hex convenient for looking at raw memory and addresses. You’ve probably seen it in hexdumps. Here’s a hexdump of the first 256 bytes of this site’s favicon.ico (a WEBP in disguise):

00000000: 5249 4646 e603 0000 5745 4250 5650 384c  RIFF....WEBPVP8L
00000010: d903 0000 2f17 c005 1035 c9cd b66d 9514  ..../....5...m..
00000020: 3b3e 6e6b e38b bbbb bb13 4903 9aba 3b64  ;>nk......I...;d
00000030: 50c5 9291 6944 e47e e697 7366 a6a1 b516  P...iD.~..sf....
00000040: fe90 026c 8a40 23ba d036 b8c8 c9dc b36d  ...l.@#..6.....m
00000050: 002d 6773 3252 3bd9 5a46 037a aad8 1ac8  .-gs2R;.ZF.z....
00000060: 2842 27c3 a229 614a d874 236a d026 f622  (B'..)aJ.t#j.&."
00000070: dd22 b856 aa98 0492 6dbb 6d9b 0f8b 944f  .".V....m.m....O
00000080: 7aef 7d56 a7d9 ff34 1be9 c576 e443 fc43  z.}V...4...v.C.C
00000090: 1380 20d9 b6db b601 a40f 0120 e9a6 92e2  .. ........ ....
000000a0: 3eca fe47 d943 7690 7d34 c945 50ff 2780  >..G.Cv.}4.EP.'.
000000b0: 640f 6c01 ab59 14f7 39fc 641f 95e4 1658  d.l..Y..9.d....X
000000c0: 6c61 609d 9045 0102 1560 b244 06d6 880e  la`..E...`.D....
000000d0: 5135 47b0 8da2 85f5 96bc b7cb fa99 aa05  Q5G.............
000000e0: 0592 2a74 4065 a0fa c8b7 6c72 00db 0dda  ..*t@e....lr....
000000f0: 3323 cff5 1e7f ec77 bf9e d3a7 9f81 2d80  3#.....w......-.

Readable ASCII runs from 0x20 (space) to 0x7E (~); 0x7F is DEL, a control character.