rogrammers' Day is an international unofficial professional holiday that is also officially recognized in Russia, celebrated on the 256th (0x100th) day of each year (13 September during common years and on 12 September in leap years).
The number 256 was chosen because it is the number of distinct values that can be represented with an eight-bit byte—a number that is typically very well known to programmers. Starting from zero, the 256th value represented by a sequential permutation of 8 bits is an unsigned integer 255 or hexadecimal 0xff or binary 0b11111111. 256 is the highest power of two that is less than 365, the number of days in a common year.
By the same logic, the white colour was chosen because it represents a hex number with the largest value in a 24-bit red green blue (RGB) color space: 0xFFFFFF, so programmers worldwide wear white at celebration.
This particular day was proposed by Valentin Balt, an employee of Parallel Technologies web design company. As early as 2002 he tried to gather signatures for a petition to the Government of Russia to recognize the day as the official programmers' day.
On July 24, 2009, the Ministry of Mass Communications of Russia issued a draft of an executive order on a new professional holiday, Programmers' Day.
On September 11, 2009, the President of Russia, Dmitry Medvedev signed the decree.