System time

In computer science and computer programming, system time represents a computer system's notion of the passage of time. In this sense, time also includes the passing of days on the calendar.

System time is measured by a system clock, which is typically implemented as a simple count of the number of ticks that have transpired since some arbitrary starting date, called the epoch. For example, Unix and POSIX-compliant systems encode system time ("Unix time") as the number of seconds elapsed since the start of the Unix epoch at 1 January 1970 00:00:00 UT, with exceptions for leap seconds. Systems that implement the 32-bit and 64-bit versions of the Windows API, such as Windows 9x and Windows NT, provide the system time as both SYSTEMTIME, represented as a year/month/day/hour/minute/second/milliseconds value, and FILETIME, represented as a count of the number of 100-nanosecond ticks since 1 January 1601 00:00:00 UT as reckoned in the proleptic Gregorian calendar.

System time can be converted into calendar time, which is a form more suitable for human comprehension. For example, the Unix system time 1000000000 seconds since the beginning of the epoch translates into the calendar time 9 September 2001 01:46:40 UT. Library subroutines that handle such conversions may also deal with adjustments for timezones, daylight saving time (DST), leap seconds, and the user's locale settings. Library routines are also generally provided that convert calendar times into system times.

Unix date command

Other time measurements

Closely related to system time is process time, which is a count of the total CPU time consumed by an executing process. It may be split into user and system CPU time, representing the time spent executing user code and system kernel code, respectively. Process times are a tally of CPU instructions or clock cycles and generally have no direct correlation to wall time.

File systems keep track of the times that files are created, modified, and/or accessed by storing timestamps in the file control block (or inode) of each file and directory.


Most first-generation personal computers did not keep track of dates and times. These included systems that ran the CP/M operating system, as well as early models of the Apple II, the BBC Micro, and the Commodore PET, among others. Add-on peripheral boards that included real-time clock chips with on-board battery back-up were available for the IBM PC and XT, but the IBM AT was the first widely available PC that came equipped with date/time hardware built into the motherboard. Prior to the widespread availability of computer networks, most personal computer systems that did track system time did so only with respect to local time and did not make allowances for different time zones.

With current technology, most modern computers keep track of local civil time, as do many other household and personal devices such as VCRs, DVRs, cable TV receivers, PDAs, pagers, cell phones, fax machines, telephone answering machines, cameras, camcorders, central air conditioners, and microwave ovens.

Microcontrollers operating within embedded systems (such as the Raspberry Pi, Arduino, and other similar systems) do not always have internal hardware to keep track of time. Many such controller systems operate without knowledge of the external time. Those that require such information typically initialize their base time upon rebooting by obtaining the current time from an external source, such as from a time server or external clock, or by prompting the user to manually enter the current time.


The system clock is typically implemented as a programmable interval timer that periodically interrupts the CPU, which then starts executing a timer interrupt service routine. This routine typically adds one tick to the system clock (a simple counter) and handles other periodic housekeeping tasks (preemption, etc.) before returning to the task the CPU was executing before the interruption.

Retrieving system time

The following tables illustrate methods for retrieving the system time in various operating systems, programming languages, and applications. Values marked by (*) are system-dependent and may differ across implementations. All dates are given as Gregorian or proleptic Gregorian calendar dates.

Note that the resolution of an implementation's measurement of time does not imply the same precision of such measurements. For example, a system might return the current time as a value measured in microseconds, but actually be capable of discerning individual clock ticks with a frequency of only 100 Hz (10 ms).

Operating systems

Operating system Command or function Resolution Epoch or range
Android java.lang.System.currentTimeMillis() 1 ms 1 January 1970
BIOS (IBM PC) INT 1Ah, AH=00h[1] 54.9254 ms
18.2065 Hz
Midnight of the current day
INT 1Ah, AH=02h[2] 1 s Midnight of the current day
INT 1Ah, AH=04h[3] 1 day 1 January 1980 to 31 December 1999 or 31 December 2079 (system dependent)
CP/M Plus System Control Block:[4]
scb$base+58h, Days since 1 Jan 1978
scb$base+5Ah, Hour (BCD)
scb$base+5Bh, Minute (BCD)
scb$base+5Ch, Second (BCD)
1 s 1 January 1978 to September 2067
BDOS function 69h (T_GET):[5]
word, Days since 1 January 1978
byte, Hour (BCD)
byte, Minute (BCD)
byte, Second (BCD)
DOS (Microsoft) C:\>DATE
10 ms 1 January 1980 to 31 December 2099
iOS (Apple) CFAbsoluteTimeGetCurrent()[8] < 1 ms 1 January 2001 ±10,000 years
macOS CFAbsoluteTimeGetCurrent()[9] < 1 ms[10][note 1] 1 January 2001 ±10,000 years[10][note 1]
OpenVMS SYS$GETTIM() 100 ns 17 November 1858 to AD 31,086
z/OS STCK[11] 2−12 μs
244.14 ps[12]
1 January 1900 to 17 September 2042 UT[13]
(see also C date and time functions)
1 s (*)
1 January 1970 to 19 January 2038
1 January 1970 to AD 292,277,026,596
gettimeofday() 1 μs
clock_gettime() 1 ns
OS/2 DosGetDateTime() 10 ms 1 January 1980 to 31 December 2079[14]
Windows GetSystemTime() 1 ms 1 January 1601 to AD 30,828
GetSystemTimeAsFileTime() 100 ns

Programming languages and applications

Language/Application Function or variable Resolution Epoch or range
Ada Ada.Calendar.Clock 100 μs to
20 ms (*)
1 January 1901 to 31 December 2099 (*)
AWK systime() 1 s (*)
1 s (*)
Business BASIC DAY, TIM 0.1 s (*)
C (see C date and time functions) time() 1 s (*)[note 2] (*)[note 2]
C++ std::time()
1 s (*)[note 2]
1 ns (C++11, OS dependent)
(*)[note 2]
C# System.DateTime.Now[15]
100 ns[17] 1 January 0001 to 31 December 9999
CICS ASKTIME 1 ms 1 January 1900
Common Lisp (get-universal-time) 1 s 1 January 1900
Delphi (Borland) date
1 ms
(floating point)
1 January 1900
(Embarcadero Technologies)[18]
System.SysUtils.Time[19] 1 ms 0/0/0000 0:0:0:000 to 12/31/9999 23:59:59:999 [sic]
System.SysUtils.GetTime[20] (alias for System.SysUtils.Time)
System.SysUtils.Date[21] 0/0/0000 0:0:0:000 to 12/31/9999 0:0:0:000 [sic]
System.SysUtils.Now[25] 1 s 0/0/0000 0:0:0:000 to 12/31/9999 23:59:59:000 [sic]
System.SysUtils.DayOfWeek[26] 1 day 1 to 7
System.SysUtils.CurrentYear[27] 1 year (*)
Emacs Lisp (current-time) 1 μs (*) 1 January 1970
Erlang erlang:system_time(), os:system_time()[28] OS dependent, e.g. on Linux 1ns[28] 1 January 1970[28]
Excel date() ? 0 January 1900[29]


1 January 1970
Go time.Now() 1 ns 1 January 0001
Haskell Time.getClockTime 1 ps (*) 1 January 1970 (*)
Data.Time.getCurrentTime 1 ps (*) 17 November 1858 (*)
Java java.util.Date()
1 ms 1 January 1970
System.nanoTime()[32] 1 ns arbitrary[32]
Clock.systemUTC()[33] 1 ns arbitrary[34]
JavaScript, TypeScript (new Date()).getTime()
1 ms 1 January 1970
Matlab now 1 s 0 January 0000[35]
MUMPS $H (short for $HOROLOG) 1 s 31 December 1840
LabVIEW Tick Count 1 ms 00:00:00.000 1 January 1904
Get Date/Time in Seconds 1 ms 00:00:00.000 1 January 1904
Objective-C [NSDate timeIntervalSinceReferenceDate] < 1 ms[36] 1 January 2001 ±10,000 Years[36]
OCaml Unix.time() 1 s 1 January 1970
Unix.gettimeofday() 1 μs
Extended Pascal GetTimeStamp() 1 s (*)
Turbo Pascal GetTime()
10 ms (*)
Perl time() 1 s 1 January 1970
Time::HiRes::time[37] 1 μs
PHP time()
1 s 1 January 1970
microtime() 1 μs
Python 1 μs (*) 1 January 1970
1 s 1 January 0001 to 31 December 9999
Ruby[38] 1 μs (*) 1 January 1970 (to 19 January 2038 prior to Ruby 1.9.2[39])
Smalltalk Time microsecondClock
1 s (ANSI)
1 μs (VisualWorks)
1 s (Squeak)
1 January 1901 (*)
Time totalSeconds
SystemClock ticksNowSinceSystemClockEpoch
3 ms 1 January 1753 to 31 December 9999 (*)
60 s 1 January 1900 to 6 June 2079
Standard ML 1 μs (*) 1 January 1970 (*)
TCL [clock seconds] 1 s 1 January 1970
[clock milliseconds] 1 ms
[clock microseconds] 1 μs
[clock clicks] 1 μs (*) (*)
Windows PowerShell Get-Date[40][41] 100 ns[17] 1 January 0001 to 31 December 9999
Visual Basic .NET System.DateTime.Now[15]
100 ns[17] 1 January 0001 to 31 December 9999

See also


  1. ^ a b The Apple Developer Documentation is not clear on the precision & range of CFAbsoluteTime/CFTimeInterval, except in the CFRunLoopTimerCreate documentation which refers to 'sub-millisecond at most' precision. However, the similar type NSTimeInterval appears to be interchangeable, and has the precision and range listed.
  2. ^ a b c d The C standard library does not specify any specific resolution, epoch, range, or datatype for system time values. The C++ library encompasses the C library, so it uses the same system time implementation as C.


  1. ^ Ralf D. Brown, "Int 0x1A, AH=0x00" in Ralf Brown's Interrupt List, 2000,
  2. ^ Ralf D. Brown, "Int 0x1A, AH=0x02" in Ralf Brown's Interrupt List, 2000,
  3. ^ Ralf D. Brown, "Int 0x1A, AH=0x04" in Ralf Brown's Interrupt List, 2000,
  4. ^ "CP/M Plus (CP/M Version 3.0) Operating System Guide" (PDF).
  5. ^ "BDOS system calls".
  6. ^ Ralf D. Brown, "Int 0x21, AH=0x2c" in Ralf Brown's Interrupt List, 2000,
  7. ^ Ralf D. Brown, "Int 0x21, AH=0x2a" in Ralf Brown's Interrupt List, 2000,
  8. ^ "Time Utilities Reference" in iOS Developer Library (Apple, 2007).
  9. ^ "Time Utilities Reference" in Mac OS X Developer Library (Apple, 2007).
  10. ^ a b "CFRunLoopTimer Reference" in Mac OS X Developer Library (Apple, 2007).
  11. ^ z/Architecture Principles of Operation (Poughkeepsie, New York:International Business Machines, 2007) 7-187.
  12. ^ z/Architecture Principles of Operation, (Poughkeepsie, New York:International Business Machines, 2000) 4-45, 4-46.
  13. ^ IBM intends to extend the date range on future systems beyond 2042. z/Architecture Principles of Operation, (Poughkeepsie, New York:International Business Machines, 2007) 1-15, 4-45 to 4-47.
  14. ^ "On OS/2 Warp 4, date and time can both operate well beyond the year 2000, and even well beyond the year 2038, and in fact up to the year 2079, which is the limit for OS/2 Warp 4's real-time clock." [1] The 32-bit Command Interpreter by Jonathan de Boyne Pollard
  15. ^ a b c "DateTime.Now Property" in MSDN (Microsoft, 2010) last updated July 2010.
  16. ^ a b c "DateTime.UtcNow Property" in MSDN (Microsoft, 2011)
  17. ^ a b c "DateTime.Ticks Property in MSDN (Microsoft, 2010) last updated May 2010.
  18. ^ "Date and Time Support" in Embarcadero Developer Network (Embarcadero Technologies, 2013)
  19. ^ "System.SysUtils.Time" in Embarcadero Developer Network (Embarcadero Technologies, 2013)
  20. ^ "System.SysUtils.GetTime" in Embarcadero Developer Network (Embarcadero Technologies, 2013)
  21. ^ "System.SysUtils.Date" in Embarcadero Developer Network (Embarcadero Technologies, 2013)
  22. ^ "System.DateUtils.Today" in Embarcadero Developer Network (Embarcadero Technologies, 2013)
  23. ^ "System.DateUtils.Tomorrow" in Embarcadero Developer Network (Embarcadero Technologies, 2013)
  24. ^ "System.DateUtils.Yesterday" in Embarcadero Developer Network (Embarcadero Technologies, 2013)
  25. ^ "System.SysUtils.Now" in Embarcadero Developer Network (Embarcadero Technologies, 2013)
  26. ^ "System.SysUtils.DayOfWeek" in Embarcadero Developer Network (Embarcadero Technologies, 2013)
  27. ^ "System.SysUtils.CurrentYear" in Embarcadero Developer Network (Embarcadero Technologies, 2013)
  28. ^ a b c Time and Time Correction in Erlang
  29. ^ "In the Microsoft Office Spreadsheet Component, the value 0 evaluates to the date December 30, 1899 and the value 1 evaluates to December 31, 1899. ... In Excel, the value 0 evaluates to January 0, 1900 and the value 1 evaluates to January 1, 1900." XL2000: Early Dates on Office Spreadsheet Component Differ from Excel in (Microsoft Support, 2003).
  30. ^ "SYSTEM_CLOCK", documentation for FORTRAN compiler, Intel Corp., accessed 27 October 2011.
  31. ^ SYSTEM_CLOCK — Time function" in The GNU Fortran Compiler (Free Software Foundation) accessed 27 October 2011.
  32. ^ a b System.nanoTime() method in Java Platform, Standard Edition 6: API Specification (Oracle, 2011) accessed 27 October 2011.
  33. ^ Clock.systemUTC() and other methods in Java Platform, Standard Edition 8: API Specification (Oracle, 2014) accessed 15 January 2015.
  34. ^ JSR-310 Java Time System in Java Platform, Standard Edition 8: API Specification (Oracle, 2014) accessed 15 January 2015.
  35. ^ [2] Matlab Help
  36. ^ a b "Foundation Data Types Reference" in Mac OS X Developer Library (Apple, 2011) last modified 6 July 2011, section NSTimeInterval.
  37. ^ Douglas Wegscheild, R. Schertler, and Jarkko Hietaniemi, "Time::HiRes" (CPAN Comprehensive Perl Archive Network, 2011) accessed 27 October 2011.
  38. ^ Time class in Help and documentation for the Ruby programming language (Scottsdale, AZ: James Britt and Neurogami) accessed 27 October 2011.
  39. ^ Ruby 1.9.2 Release Notes in Help and documentation for the Ruby programming language (Scottsdale, AZ: James Britt and Neurogami) accessed 27 October 2011.
  40. ^ "Using the Get-Date Cmdlet". Microsoft TechNet. Retrieved 11 December 2013.
  41. ^ "Windows PowerShell Tip of the Week – Formatting Dates and Times". Microsoft TechNet. Retrieved 11 December 2013.

External links

Adam Rodriguez

Adam Michael Rodriguez (born April 2, 1975) is an American actor, screenwriter and director. He became known for his long running role as Eric Delko on CSI: Miami. He is currently portraying Task Force Agent and the newest recruit to the BAU, Agent Luke Alvez in Criminal Minds.

Carol Burnett

Carol Creighton Burnett (born April 26, 1933) is an American actress, comedian, singer and writer, whose career spans seven decades of television. She is best known for her groundbreaking comedy variety show, The Carol Burnett Show, originally aired on CBS. It was the first of its kind to be hosted by a woman. She has achieved success on stage, television and film in varying genres including dramatic and comedic roles. She has also appeared on various talk shows and as a panelist on game shows.

Born in San Antonio, Texas, Burnett moved with her grandmother to Hollywood, where she attended Hollywood High School and eventually studied theater and musical comedy at UCLA. Later she performed in nightclubs in New York City and had a breakout success on Broadway in 1959 in Once Upon a Mattress, for which she received a Tony Award nomination. She soon made her television debut, regularly appearing on The Garry Moore Show for the next three years, and won her first Emmy Award in 1962. Burnett had her television special debut in 1963 when she starred as Calamity Jane in the Dallas State Fair Musicals production of Calamity Jane on CBS. Burnett moved to Los Angeles, California, and began an 11-year run as star of The Carol Burnett Show on CBS television from 1967 to 1978. With its vaudeville roots, The Carol Burnett Show was a variety show that combined comedy sketches with song and dance. The comedy sketches included film parodies and character pieces. Burnett created many memorable characters during the show's run, and both she and the show won numerous Emmy and Golden Globe Awards.

During and after her variety show, Burnett appeared in many television and film projects. Her film roles include Pete 'n' Tillie (1972), The Front Page (1974), The Four Seasons (1981), Annie (1982), Noises Off (1992), and Horton Hears a Who! (2008). On television, she has appeared in other sketch shows; in dramatic roles in 6 Rms Riv Vu (1974) and Friendly Fire (1979); in various well-regarded guest roles, such as in Mad About You, for which she won an Emmy Award; and in specials with Julie Andrews, Dolly Parton, Beverly Sills, and others. She returned to the Broadway stage in 1995 in Moon Over Buffalo, for which she was again nominated for a Tony Award.

Burnett has written and narrated several memoirs, earning Grammy nominations for almost all of them, and a win for In Such Good Company: Eleven Years Of Laughter, Mayhem, And Fun In The Sandbox.In 2005, she was recognized as "one of America's most cherished entertainers" and awarded the Presidential Medal of Freedom "for enhancing the lives of millions of Americans and for her extraordinary contributions to American entertainment."

Chiasmus (cipher)

Chiasmus is a secret German government block cipher that was leaked by reverse engineering. It became notorious for its dilettant use in the BSI's software GSTOOL, which used it in insecure Electronic Codebook (ECB) mode and generated the key with a pseudo random number generator initialized to the current system time, which means an effective key length that can easily be broken by brute force. The BSI tried to prevent the publication of these findings with legal threats.

Chiasmus seems to be resistant against the most common cryptographic attacks (linear and differential cryptanalysis), but a lot slower than the openly available state of the art ciphers such as AES.

Doris Roberts

Doris May Roberts (born Doris May Green; November 4, 1925 – April 17, 2016) was an American actress, author, and philanthropist whose career spanned six decades of television and film. She received five Emmy Awards and a Screen Actors Guild award during her acting career, which began in 1951.

Roberts studied acting at The Neighborhood Playhouse School of the Theatre in New York City and started in films in 1961. She had several prominent roles in movies, including playing opposite Shirley Stoler in The Honeymoon Killers (1970), Elliott Gould in Little Murders (1971), Steven Keats in Hester Street (1975), Billy Crystal in Rabbit Test (1978), Robert Carradine in Number One with a Bullet (1987), and Cady McClain in Simple Justice (1989), among many others.

She achieved continuing success in television, becoming known for her role as Mildred Krebs in Remington Steele from 1983 to 1987 and her co-starring role as Raymond Barone's mother, Marie Barone, on the long-running CBS sitcom Everybody Loves Raymond (1996–2005). Towards the end of her acting career, she also had a prominent role opposite Tyler Perry in Madea's Witness Protection (2012).

She appeared as a guest on many talk and variety shows, along with appearing as a panelist on several game shows. She was an advocate of animal rights and animal-rights activism, supporting groups such as the United Activists for Animal Rights.

Galileo (satellite navigation)

Galileo is the global navigation satellite system (GNSS) that went live in 2016, created by the European Union (EU) through the European GNSS Agency (GSA), headquartered in Prague in the Czech Republic, with two ground operations centres, Oberpfaffenhofen near Munich in Germany and Fucino in Italy. The €10 billion project is named after the Italian astronomer Galileo Galilei. One of the aims of Galileo is to provide an independent high-precision positioning system so European nations do not have to rely on the U.S. GPS, or the Russian GLONASS systems, which could be disabled or degraded by their operators at any time.

The use of basic (lower-precision) Galileo services will be free and open to everyone. The higher-precision capabilities will be available for paying commercial users. Galileo is intended to provide horizontal and vertical position measurements within 1-metre precision, and better positioning services at higher latitudes than other positioning systems.

Galileo is also to provide a new global search and rescue (SAR) function as part of the MEOSAR system.

The first Galileo test satellite, the GIOVE-A, was launched 28 December 2005, while the first satellite to be part of the operational system was launched on 21 October 2011. As of July 2018, 26 of the planned 30 active satellites are in orbit. Galileo started offering Early Operational Capability (EOC) on 15 December 2016, providing initial services with a weak signal, and is expected to reach Full Operational Capability (FOC) in 2019. The complete 30-satellite Galileo system (24 operational and 6 active spares) is expected by 2020. It is expected that the next generation of satellites will begin to become operational by 2025 to replace older equipment. Older systems can then be used for backup capabilities.

There are 22 satellites in usable condition (satellite is operational and contributing to the service provision), 2 satellites are in "testing" and 2 more are marked as not available.

Genie Francis

Eugenie Ann Francis Frakes (born May 26, 1962) is an American actress best known for her portrayal of Laura Spencer on the ABC Daytime soap opera General Hospital.


Horology ("the study of time", related to Latin horologium from Greek ὡρολόγιον, "instrument for telling the hour", from ὥρα hṓra "hour; time" and -o- interfix and suffix -logy) is the study of the measurement of time. Clocks, watches, clockwork, sundials, hourglasses, clepsydras, timers, time recorders, marine chronometers, and atomic clocks are all examples of instruments used to measure time. In current usage, horology refers mainly to the study of mechanical time-keeping devices, while chronometry more broadly includes electronic devices that have largely supplanted mechanical clocks for the best accuracy and precision in time-keeping.

People interested in horology are called horologists. That term is used both by people who deal professionally with timekeeping apparatus (watchmakers, clockmakers), as well as aficionados and scholars of horology. Horology and horologists have numerous organizations, both professional associations and more scholarly societies. The largest horological membership organisation globally is the NAWCC, the National Association of Watch and Clock Collectors, which is USA based, but also has local chapters elsewhere.

Intercalation (timekeeping)

Intercalation or embolism in timekeeping is the insertion of a leap day, week, or month into some calendar years to make the calendar follow the seasons or moon phases. Lunisolar calendars may require intercalations of both days and months.

James Patrick Stuart

James Patrick Stuart (born June 16, 1968) is an American actor and voice actor, currently portraying Valentin Cassadine on the daytime soap opera General Hospital.

Janis Paige

Janis Paige (born Donna Mae Tjaden; September 16, 1922) is an American actress and singer.

Lego Time Travels

Time Cruisers and Time Twisters compose the Lego System Time Travel theme.

The Time Cruisers are the protagonists of Lego Time Travels. Dr. Cyber and his assistant Tim visit other time periods to gather knowledge and repair damage wrought by the Time Twisters. Their primary objective is to remain undercover and meddle as little as possible with history.

Marie Wilson (American actress)

Marie Wilson (born Katherine Elizabeth Wilson; August 19, 1916 – November 23, 1972) was an American radio, film, and television actress. She may be best remembered as the title character in My Friend Irma.

Mario Cantone

Mario Cantone (born December 9, 1959) is an American comedian, writer and actor, with numerous appearances on Comedy Central including Chappelle's Show. He also played Anthony Marentino on Sex and the City. His style is fast-paced and energetic, with much of his humor coming from his impersonations of various characters ranging from his family members, to celebrities, to stereotypes.

Nancy Kulp

Nancy Jane Kulp (August 28, 1921 – February 3, 1991) was an American character actress best known as Miss Jane Hathaway on the CBS television series The Beverly Hillbillies.

Robert Vaughn

Robert Francis Vaughn (November 22, 1932 – November 11, 2016) was an American actor noted for his stage, film and television work. His best-known television roles include suave spy Napoleon Solo in the 1960s series The Man from U.N.C.L.E.; wealthy detective Harry Rule in the 1970s series The Protectors; Morgan Wendell in the 1978–79 mini series Centennial; formidable General Hunt Stockwell in the fifth season of the 1980s series The A-Team; and grifter and card sharp Albert Stroller in the British television drama series Hustle (2004–2012), for all but one of its 48 episodes. He also appeared in the British soap opera Coronation Street as Milton Fanshaw, a love interest for Sylvia Goodwin between January and February 2012.In film, he portrayed quiet, skittish gunman Lee in The Magnificent Seven, Major Paul Krueger in The Bridge at Remagen, the voice of Proteus IV, the computer villain of Demon Seed, Walter Chalmers in Bullitt, Ross Webster in Superman III, General Woodbridge in The Delta Force, and war veteran Chester A. Gwynn in The Young Philadelphians, which earned him a 1960 Academy Award nomination for Best Supporting Actor.

TIME (command)

In computing, TIME is a command in DOS, OS/2, Microsoft Windows and ReactOS that is used to display and set the current system time of the operating system. It is included in command-line interpreters (shells) such as COMMAND.COM, CMD.EXE, 4DOS, 4OS2 and 4NT.

The command is also available in the DEC RT-11 operating system and in the EFI shell.

In Unix, the date command displays and sets both the time and date, in a similar manner.

Time (Unix)

In computing, time is a command in Unix and Unix-like operating systems. It is used to determine the duration of execution of a particular command.

Time zone

A time zone is a region of the globe that observes a uniform standard time for legal, commercial, and social purposes. Time zones tend to follow the boundaries of countries and their subdivisions because it is convenient for areas in close commercial or other communication to keep the same time.

Most of the time zones on land are offset from Coordinated Universal Time (UTC) by a whole number of hours (UTC−12:00 to UTC+14:00), but a few zones are offset by 30 or 45 minutes (e.g. Newfoundland Standard Time is UTC−03:30, Nepal Standard Time is UTC+05:45, and Indian Standard Time is UTC+05:30).

Some higher latitude and temperate zone countries use daylight saving time for part of the year, typically by adjusting local clock time by an hour. Many land time zones are skewed toward the west of the corresponding nautical time zones. This also creates a permanent daylight saving time effect.

Key concepts
Measurement and
  • Religion
  • Mythology
Philosophy of time
Human experience
and use of time
Time in
Related topics
International standards
Obsolete standards
Time in physics
Archaeology and geology
Astronomical chronology
Other units of time
Related topics

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.