255 (number)
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255 (two hundred [and] fifty-five, CCLV) is the natural number following 254 and preceding 256. Its factorization makes it a sphenic number. It is a self number.
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| Cardinal | Two hundred [and] fifty-five |
| Ordinal | 255th |
| Factorization | <math>255 = 3 \cdot 5 \cdot 17<math> |
| Roman numeral | CCLV |
| Binary | 11111111 |
| Hexadecimal | FF |
In computing
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:
- There are exactly 255 levels in Pac-Man.
- In The Legend of Zelda, the maximum number of rupees you may have at one time is 255.
- In Super Mario Bros., the maximum amount of lives you can possess is exactly 255. The game does not check if this number is exceeded; getting another life makes all of them disappear.
- In Warcraft II, the maximum mana for any magic unit is 255.
- In Pokemon, although the limit on levels is 100; you can exceed it with a cheat code. Passing level 255 results in the number resetting to 0; however your stats are not reset.
The usage of 8 bits for storage in older videogames has had the consequence of it appearing as a hard limit in many videogames. It was often used for numbers where casual gameplay would not cause anyone to exceed the number. However in most situations it is reachable given enough time. This can cause many other pecularities similar to the above listed to appear when the number wraps back to 0.
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 (a Mersenne number). These represent the upper limit on 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.
In other fields
255 is also: