by Darius Kazemi, Feb 3 2019
Absolute and relative time
RFC-34 is titled “Some Brief Preliminary Notes on the ARC Clock”, by Bill English, dated February 26th, 1970. It continues the clock conversation we find in RFCs 28, 29, and 32.
The technical content
The ARC in “ARC clock” refers to SRI/ARC, the Stanford Research Institute's Augmentation Research Center. So in the previous RFC discussions where the “SRI clock” is referenced, I'm assuming that's the same clock as we're talking about here.
English defines absolute time as two 24-bit words (chunks of memory), where one word holds the month, day, and year. The other word holds the hour, minute, and second. Relative time is just a number that ticks up once every 1 millisecond or sometimes once every 0.1 milliseconds, and is relative to whenever you initially set it, kind of like a stopwatch.
English claims that oscillator drift will accumulate not more than 1 second of error every 250 days. That's... really accurate, and is on the same order of magnitude I calculated in the Analysis section of my post on RFC-32.
At the time of these RFCs, SRI was a Stanford University affiliated nonprofit known as the Stanford Research Institute, but right around the time these RFCs were being written, it was formally separated from Stanford University and eventually became known as SRI International. The split was apparently motivated by students protesting Stanford's role in the Vietnam War; the institute took millions in defense funding and was, according to historian Stuart W. Leslie, seen as a symbol of the US military's presence on the school campus. For more, you can read this chapter from Leslie's 1993 book The Cold War and American Science: The Military-Industrial-Academic Complex at MIT and Stanford.
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