[LEAPSECS] presentations from AAS Future of Time sessions

[Warner Losh]

On Jan 13, 2014, at 7:49 AM, Tony Finch wrote:

> Brooks Harris <brooks at edlmax.com> wrote:

> 

>> You are saying that UTC as a term for the adjusted timescale existed as

>> the process of time-keeping in computers began and they intended

>> computers to reflect "civil time" even if the details of exactly how to

>> do that hadn't been worked out. "Modern" UTC, UTC with Leap Seconds

>> after 1972, hadn't yet started, so it wasn't considered.

> 

> The development was concurrent, not sequential. Unix 1st and 2nd edition

> had a 1971 epoch and 1/60th second resolution. 3rd edition moved the epoch

> to 1972. (The overall manual was dated Feb 1973 and the page for time(2)

> was dated March 1972.) The 4th edition introduced modern Unix time.

> (Overall manual dated November 1973, and time(2) dated August 1973.)

> 

> So UTC had started but wasn't available to the computers that Unix was

> running on.


The precision of the time in Unix was sub-second, but given all accounts of the time, and my experience with systems a decade later, I'd be very much surprised if the accuracy of the system time was better than sub-minute since a synchronization Dennis' wrist-watch was involved. Given how well computers I used in the early 80's maintained time, I'd imagine the synchronization a decade earlier likely was a regular occurrence...

Warner