Binary, hex and characters

In decimal each place is worth ten times the place on its right. In binary each place is worth two times the place on its right, so the places of 8 bits are 128, 64, 32, 16, 8, 4, 2, 1. To read a binary number, add the place values where the digit is 1: 1011 0101 is 128 + 32 + 16 + 4 + 1 = 181. To write a decimal number in binary, divide by 2 again and again and keep the remainders; read them from the last to the first. For 37: 37 ÷ 2 = 18 remainder 1, 18 ÷ 2 = 9 r 0, 9 ÷ 2 = 4 r 1, 4 ÷ 2 = 2 r 0, 2 ÷ 2 = 1 r 0, 1 ÷ 2 = 0 r 1; reading upward gives 100101. Binary numbers get long, so people use hexadecimal, which has 16 digits: 0 to 9 and then A = 10, B = 11, C = 12, D = 13, E = 14, F = 15. One hex digit stands for exactly four bits. To convert, cut the bits into groups of four, starting at the right-hand end: 1010 0111 is A and 7, so A7. Check: A7 = 10 × 16 + 7 = 167, and 1010 0111 = 128 + 32 + 4 + 2 + 1 = 167. The biggest byte, 1111 1111, is FF = 255. Colour codes on web pages are written in hex.