jiffy (time)

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 vacuum (approximately 33.3564 picoseconds).

{{cite web

| url= http://www.numericana.com/answer/units.htm#jiffy

| title= What's a jiffy?

| author= Gerard P. Michon

| date= November 2002

| work= Units of Measurement

| publisher= Numericana

| access-date= 2008-12-30

}}

It has since been redefined for different measurements depending on the field of study.

{{cite web

|author=Russ Rowlett

|date=September 2001

|title=jiffy

|url=http://www.unc.edu/~rowlett/units/dictJ.html

|access-date=2009-08-31

|work=How Many? A Dictionary of Units of Measurement

|publisher=University of North Carolina

}}

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.{{cite web|url=https://lwn.net/Articles/549593/ |title=Documentation/timers/NO_HZ.txt (3.10) |date=May 7, 2013}} It is not an absolute time interval unit, since its duration depends on the clock interrupt frequency of the particular hardware platform.{{cite web |title=time(7) - Linux manual page |url=http://man7.org/linux/man-pages/man7/time.7.html |website=man7.org}}{{dubious|reason=set by software on at least some platforms e.g. i386 Linux at compile time, runtime variable on Windows, plus we're now in an era of tickless kernels using higher resolution timers to provide the same feature in a dynamic way|date=October 2013}}

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.{{Citation needed|date=March 2023}}

Some 1980s 8-bit Commodore computers, such as the PET / VIC-20 / C64, had a jiffy of 1/60 second, which was not dependent on the mains AC or video vertical refresh rate.{{cite web |title=TIME |url=https://www.c64-wiki.com/wiki/TIME |website=C64 Wiki |archive-url=https://web.archive.org/web/20230302044648/https://www.c64-wiki.com/wiki/TIME |archive-date=2023-03-02 |url-status=live }} A timer in the computer creates the 60 Hz rate, causing an interrupt service routine to be executed every 1/60 second, incrementing a 24-bit jiffy counter, scanning the keyboard, and handling some other housekeeping.{{cite web |title=How the C64 Keyboard Works |url=https://c64os.com/post/howthekeyboardworks |website=C64 OS |archive-url=https://web.archive.org/web/20230302051942/https://c64os.com/post/howthekeyboardworks |archive-date=March 2, 2023 |date=October 23, 2017 |url-status=live }}

Jiffy values for various Linux versions and platforms have typically varied between about 1 ms and 10 ms, with 10 ms (1/100 s) reported as an increasingly common standard in the Jargon File.[http://catb.org/~esr/jargon/html/J/jiffy.html Entry on jiffy] in The Jargon File

Stratus VOS (Virtual Operating System) uses a jiffy of 1/65,536 second to express date and time (number of jiffies elapsed since {{nowrap|1 January 1980 00:00 Greenwich Mean Time)}}. Stratus also defines the microjiffy, being 1/65,536 of a regular jiffy."{{cite web |title=StrataDOC - Time Intervals |url=https://stratadoc.stratus.com/vos/15.1.1/r021-08/wwhelp/wwhimpl/common/html/wwhelp.htm?context=r021-08&file=ch1r021-08m.html |access-date=2018-11-01 |publisher=Stratus}}

The term jiffy is sometimes used in computer animation as a method of defining playback rate, with the delay interval between individual frames specified in 1/100 of a second (10 ms) jiffies, particularly in Autodesk Animator .FLI sequences (one global frame frequency setting) and animated Compuserve .GIF images (each frame having an individually defined display time measured in 1/100 s).{{Citation needed|date=March 2023}}

The speed of light in vacuum provides a convenient universal relationship between distance and time, so in physics (particularly in quantum physics) and often in chemistry, a jiffy is defined as the time taken for light to travel some specified distance. In astrophysics and quantum physics a jiffy is, as defined by Edward R. Harrison,"The Cosmic Numbers" in Cosmology, The Science of the Universe, 1981 Cambridge Press the time it takes for light to travel one fermi, which is approximately the size of a nucleon. One fermi is {{val|e=-15|u=m}}, so a jiffy is about {{val|3|e=-24|u=seconds}}. It has also more informally been defined as "one light-foot", which is equal to approximately one nanosecond.

• System time
• BogoMips – which computes loops_per_jiffy
• TU (time unit)
• Orders of magnitude (time)

{{reflist|30em}}

{{Wiktionary|jiffy}}

• FOLDOC

{{Time measurement and standards}}

Jiffy

Jiffy#Use in computing

Jiffy#Use in computing