Hexadecimal, in mathematics and computer science, is a base-16 numbering system using 10 digits (0 through 9) and six letters (A through F). Used in the computer world as a shorthand way to write binary numbers, by substituting one hex digit for a four-digit binary number (for example, hex 9 = binary 1001). International Business Machines (IBM) introduced the current hexadecimal system to the computing world. An earlier version, using the digits 0–9 and the letters u–z, had been previously introduced in 1956.