Editing Time zone (section)

=== Operating systems ===
==== Unix ====
{{Main|Unix time}}

[[Unix-like]] systems, including [[Linux]] and [[macOS]], keep system time in [[Unix time]] format, representing the number of seconds that have elapsed since 00:00:00 [[Coordinated Universal Time]] (UTC) on Thursday, January 1, 1970, excluding [[leap second]]s.<ref name="single-unix-spec-4.16">{{cite web|url=http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_16|title=The Open Group Base Specifications Issue 7, section 4.16 Seconds Since the Epoch|publisher=[[The Open Group]]|access-date=January 22, 2017|archive-date=December 22, 2017|archive-url=https://web.archive.org/web/20171222113543/http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_16|url-status=live}}</ref> Unix time is usually converted to local time when displayed to the user, and times specified by the user in local time are converted to Unix time.  The conversion takes into account the time zone and daylight saving time rules; by default the time zone and daylight saving time rules are set up when the system is configured, though individual processes can specify time zones and daylight saving time rules using the ''TZ'' [[environment variable]].<ref name="tzset(3)">{{man|sh|tzset|SUS}}</ref> This allows users in multiple time zones, or in the same time zone but with different daylight saving time rules, to use the same computer, with their respective local times displayed correctly to each user. Information about time zones and daylight saving time rules most commonly comes from the [[IANA time zone database]]. Many systems, including anything using the [[GNU C Library]], a C library based on the [[BSD]] C library, or the [[System V Release 4]] C library, can make use of the IANA time zone database.

==== Microsoft Windows ====
[[Microsoft Windows|Windows]]-based computer systems prior to [[Windows 95]] and [[Windows NT]] used local time, but Windows 95 and later, and Windows NT, base system time on UTC.<ref>{{cite web|url=http://msdn2.microsoft.com/en-us/library/ms724961.aspx|title=System Time|website=[[MSDN]]|archive-url=https://web.archive.org/web/20070227230411/http://msdn2.microsoft.com/en-us/library/ms724961.aspx|archive-date=2007-02-27|url-status=dead}}</ref><ref>{{cite web|url=https://learn.microsoft.com/en-us/windows/win32/sysinfo/system-time|title=System Time|website=[[Microsoft Learn]]|date=January 7, 2021|access-date=April 23, 2024|archive-date=February 24, 2024|archive-url=https://web.archive.org/web/20240224224835/https://learn.microsoft.com/en-us/windows/win32/sysinfo/system-time|url-status=live}}</ref> They allow a program to fetch the system time as UTC, represented as a year, month, day, hour, minute, second, and millisecond;<ref>{{cite web|url=http://msdn2.microsoft.com/en-us/library/ms724390.aspx|title=GetSystemTime|website=MSDN|archive-url=https://web.archive.org/web/20070228030857/http://msdn2.microsoft.com/en-us/library/ms724390.aspx|archive-date=2007-02-28|url-status=dead}}</ref><ref>{{cite web|url=https://learn.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getsystemtime|title=GetSystemTime function (Windows)|website=Microsoft Learn|date=February 22, 2024|access-date=April 23, 2024|archive-date=April 23, 2024|archive-url=https://web.archive.org/web/20240423071349/https://learn.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getsystemtime|url-status=live}}</ref> Windows 95 and later, and Windows NT 3.5 and later, also allow the system time to be fetched as a count of 100 ns units since 1601-01-01 00:00:00 UTC.<ref>{{cite web|url=http://msdn2.microsoft.com/en-us/library/ms724397.aspx|title=GetSystemTimeAsFileTime|website=MSDN|archive-url=https://web.archive.org/web/20070224215258/http://msdn2.microsoft.com/en-us/library/ms724397.aspx|archive-date=2007-02-24|url-status=dead}}</ref><ref>{{cite web|url=https://learn.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getsystemtimeasfiletime|title=GetSystemTimeAsFileTime function (Windows)|website=Microsoft Learn|date=February 22, 2024 |access-date=April 23, 2024}}</ref> The [[Windows Registry|system registry]] contains time zone information that includes the offset from UTC and rules that indicate the start and end dates for daylight saving in each zone. Interaction with the user normally uses local time, and application software is able to calculate the time in various zones. [[Remote Desktop Services|Terminal Servers]] allow remote computers to redirect their time zone settings to the Terminal Server so that users see the correct time for their time zone in their desktop/application sessions. Terminal Services uses the server base time on the Terminal Server and the client time zone information to calculate the time in the session.