Talk:Unix time/Archives/2019

Bad Terminology: Epoch Time

I've tried a simple edit in the past, but it was undone. Basically, there are a lot of people using the term "epoch time" on other sites and pointing here as proof that it is valid. The word "epoch" is a simple English noun, and Wikipedia describes it well in Epoch (reference date), which also has a list of other epochs used in computing. By inventing this term "epoch time", we've started a vocabulary of programmers saying things like "I have an epoch of 1499289809..." which is of course erroneous, as the epoch would always be 0 of any form of timestamp, and is explicitly 1970-01-01 00:00:00 UTC for Unix Time.

Can we please remove the "epoch time" terminology and add a paragraph explaining that this usage is erroneous and should be avoided? We can leave the redirect in place so people find it. Thanks.

mj1856 (talk) 21:26, 5 July 2017 (UTC)

I've asked for a citation on UNIX/POSIX time being called "epoch time". Unless somebody can cough up such a citation - a citation not saying "well, Wikipedia links Epoch time to Unix time", as that would be a clear case of citogenesis - that claim should be removed from the article, and the redirect removed. Guy Harris (talk) 21:57, 5 July 2017 (UTC)

Two years later, it was still here. Did my best to replace it. Paradox (talk) 17:22, 16 June 2019 (UTC)

Thanks. I changed epoch time to redirect to epoch (computing) rather than Unix time. Guy Harris (talk) 19:09, 16 June 2019 (UTC)

"Start time"

It's not explained or made clear why the date of "1 January 1970" is the 'start' date for Unix.

Why that date?

Why couldn't other dates be 'set' during upgrades or the writing/coding of new programs?

Obviously, I'm not a programmer/coder and most of this article makes absolutely no sense to me.

First, it was "Y2K" (which could've easily been fixed); now it's 2036 or 2038 or 2262. 2600:8800:784:8F00:C23F:D5FF:FEC4:D51D (talk) 05:43, 14 March 2019 (UTC)

• I don't quite know myself, but I assume it's just a convenient date that roughly coincides with the origins of Unix. It hasn't always been like that, if you look at the "History" section; among other dates January 1, 1971 was a standard at one point. – John M Wolfson (talk • contribs) 03:07, 27 August 2019 (UTC)

"Why that date?" Because the developers of Unix chose it. Various pieces of software have chosen various epochs; not all of them have any particular significance (some do, some don't).

"Why couldn't other dates be 'set' during upgrades or the writing/coding of new programs?" If your program is going to process times returned by calls to the Unix operating system, the software that interprets those dates will have to interpret them as a count of seconds since that midnight UTC on that date or it will get a different answer; you can't "set" the start and have software get the right answer. Software could re-compute a value based on a different origin by adding a shift value to, or subtracting a shift value from, that value. One example, in epoch (computing), is "Apple's Cocoa framework" - that framework is part of macOS, which is a Unix system, but it converts Unix time to time relative to 2001-01-01).

"First, it was "Y2K" (which could've easily been fixed)" It is fixed in many of the systems that had the problem; not all did.

"now it's 2036 or 2038" 2038 is a similar, but different, problem, on systems that use UNIX-style time and store the count of seconds in a signed 32-bit value. Many UNIX systems solved it by the simple expedient of storing the count of seconds in a 64-bit value, instead - Apple's OSes store it in a 64-bit value in most file systems and in 64-bit applications, so only 32-bit applications have a Y2.038K issue, and Apple are no longer supporting those in iOS and tvOS and will not support them in macOS Catalina. Guy Harris (talk) 05:06, 27 August 2019 (UTC)

50th anniversary coming up

Hello,

The 50th anniversary of the epoch is coming up. I tagged the article as I did because I'd like to be able to get it up to the quality standards for eligibility to the main page for On This Day. I'll be doing some work on this article as my life allows. Thanks!

– John M Wolfson (talk • contribs) 21:16, 3 September 2019 (UTC)