255 (number)
- This article is about the number 255. For the year AD 255, see 255.
Two hundred fifty-five (255, CCLV) is the natural number following 254 and preceding 256. Its factorization makes it a sphenic number. It is a self number.
255 is a special number in some tasks having to do with computing. This is the maximum value representable by an eight-digit binary number, and therefore the maximum representable by an unsigned 8-bit byte (the most common size of byte, also called octet), the smallest common variable size used in high level programming languages (bit being smaller, but rarely used for value storage). The range is 0 to 255, which is 256 total values.
- <math>255 = 2^8 - 1 = \mbox{FF}_{16} = 11111111_2<math>
Due to this, this number frequently occurs in video games when a small number is needed:
Furthermore, 255 is the maximum value that can be assigned to elements in the 24-bit RGB color model.
This number could be interpreted by a computer as -1 if a programmer is not careful about which 8-bit values are signed and unsigned, and the two's complement representation of -1 in a signed byte is equal to that of 255 in an unsigned byte.
Other common numbers in computing include 127, 32767, 65535, 2147483647 and 4294967295—all of which are 2 raised to a power, minus 1. These represent signed and unsigned 8-bit, 16-bit and 32-bit numbers. The popular Intel CPUs have had registers of these sizes.
In 2003, 64-bit CPUs are gaining popularity, so expect to see the numbers 18446744073709551615 and 9223372036854775807. 128-bit numbers are larger than can be typically displayed without using scientific notation. 2127 (the maximum value of a signed 128 bit number; in 1's or 2's complement notation, it may be 1 lower) is approximately 1.7014118346046923173168730371588e+38 and 2128 is approximately 3.4028236692093846346337460743177e+38.
