Jiffy (time)

Jiffy can be an informal term for any unspecified short period, as in "I will be back in a jiffy". From this, it has acquired a number of more precise applications as the name of multiple units of measurement, each used to express or measure very brief durations of time. First attested in 1780, the word's origin is unclear, though one suggestion is that it was thieves' cant for lightning. It was common in a number of Scots English dialects and in John Jamieson's Etymological Dictionary of the Scottish Language (1808) it is suggested that it is a corruption of 'gliff' (glimpse) or 'gliffin' (glance) (compare: 'in the blink of an eye') and may ultimately derive from Gothic or Teutonic words for 'shine'. ('Gliff' or 'gliss' for 'a transient view' was also found in older English poetry as early as 1738 .) The earliest technical usage for jiffy was defined by Gilbert Newton Lewis (1875–1946). He proposed in 1926 a unit of time called the "jiffy" which was equal to the time it takes light to travel one centimeter in a vacuum (approximately 33.3564 picoseconds). It has since been redefined for different measurements depending on the field of study. In electronics, a jiffy is the period of an alternating current power cycle, 1/60 or 1/50 of a second in most mains power supplies. In computing, a jiffy was originally the time between two ticks of the system timer interrupt. It is not an absolute time interval unit, since its duration depends on the clock interrupt frequency of the particular hardware platform. Many older game consoles (which use televisions as a display device) commonly synchronize the system interrupt timer with the vertical frequency of the local television standard, either 59.94 Hz with NTSC systems, or 50.0 Hz (20 ms) with most PAL systems. 1980s 8-bit Commodore computers, such as the C64 and C128, had a jiffy of 1/60 second, which was not dependent on the mains AC or video vertical refresh rate. A timer in the computer creates the 60 Hz rate, causing an interrupt service routine to execute every 1/60 second, which increments a 24-bit jiffy counter, scans the keyboard, and some other housekeeping too.