section_path: Definition/Representing the number
section_name: Representing the number
paragraph_text: Representing the number
  
  A Unix time number can be represented in any form capable of representing numbers. In some applications the number is simply represented textually as a string of decimal digits, raising only trivial additional problems. However, certain binary representations of Unix times are particularly significant.
  
  The Unix time_t data type that represents a point in time is, on many platforms, a signed integer, traditionally of 32 bits (but see below), directly encoding the Unix time number as described in the preceding section. A signed 32-bit value covers about 68 years before and after the 1970-01-01 epoch. The minimum representable date is Friday 1901-12-13, and the maximum representable date is Tuesday 2038-01-19. One second after 2038-01-19T03:14:07Z this representation will overflow in what is known as the year 2038 problem.
  
  UUIDv 7 encodes the Unix epoch timestamp (in milliseconds) in an unsigned 48-bit field. This representation is valid until the year 10889 AD.
  
  In some newer operating systems, time_t has been widened to 64 bits. This expands the times representable to about 292.3 billion years in both directions, which is over twenty times the present age of the universe.
  
  There was originally some controversy over whether the Unix time_t should be signed or unsigned. If unsigned, its range in the future would be doubled, postponing the 32-bit overflow (by 68 years). However, it would then be incapable of representing times prior to the epoch. The consensus is for time_t to be signed, and this is the usual practice. The software development platform for version 6 of the QNX operating system has an unsigned 32-bit time_t, though older releases used a signed type.
  
  The POSIX and Open Group Unix specifications include the C standard library, which includes the time types and functions defined in the < time.h > header file. The ISO C standard states that time_t must be an arithmetic type, but does not mandate any specific type or encoding for it. POSIX requires time_t to be an integer type, but does not mandate that it be signed or unsigned.
  
  Unix has no tradition of directly representing non-integer Unix time numbers as binary fractions. Instead, times with sub-second precision are represented using composite data types that consist of two integers, the first being a time_t (the integral part of the Unix time), and the second being the fractional part of the time number in millionths (in struct timeval) or billionths (in struct timespec). These structures provide a decimal -based fixed-point data format, which is useful for some applications, and trivial to convert for others.