[netsharc]

> dumb-question: why couldn't VCRs get the time from the TV signal?

Later VCRs have that feature...

Huh, but a computer without time would be confusing indeed. A process would ask the OS, "What time is it?", "0:00", it can't even sleep for 5 seconds because the hardware clock will never tell the OS "it's 0:00:05 now" -- if the OS counts itself (doing something rudimentary like, "well it's a 1 GHz CPU, let's increment the counter every billion cycles"), then it's implemented a clock!

[DaiPlusPlus]

> Later VCRs have that feature...

…huh, turns out some US-market VCRs would automatically tune to PBS specifically for a special time-signal embedded within the TV signal, and apparently not all PBS stations participated so it would never work for some people.

I’m guessing it was something encoded into the VBI like Closed Captions and Teletext, etc? I couldn’t find the name for such a time system let alone a spec. Can you tell me where to look?

[netsharc]

Asking one of the planet-killing oracles got me this:

https://www.researchgate.net/figure/The-XDS-Line-21-Time-Cod...

[Horffupolde]

OS have millisecond uptime counters.

[LgWoodenBadger]

How does the OS know what a millisecond is without a clock?

[DaiPlusPlus]

…philosophically? Or technologically?

I’m not a philosopher; but on a technical basis, lots of OS work just fine on embedded systems that don’t provide a real-time time-of-day clock and only have time-since-booted to work on - but I don’t believe either are strictly necessary for a preemptive OS to work just fine provided the CPU itself supports millisecond-scale interrupts for the thread scheduler to work. But that made me wonder if it matters at all that a process’ time quanta have a wall-clock-based unit of quanta (e.g. people say Windows uses a 16ms quanta for foreground processes and something else (possibly variable?) for background processes. I imagine a scheduler could use a simple cpu clock cycle counter instead. Even though clock cycles themselves are also variable. And if it’s variable then it cannot be used as a clock.

…so who needs a clock? Turns out you don’t need one. I suppose that means we should just live in the present. Take each day… hour… second as it comes.

…or something. I dunno. As I said, I’m not a philosopher.

[yencabulator]

You seem to be confusing the ability to measure time passing with the knowledge of what absolute time it is.

Electronics these days measure time passing by counting oscillations of e.g. a quartz crystal. They know e.g. 16000000 oscillations is 1 second +- 0.001%. They don't know when 4pm is.

[dingnuts]

the CPU itself uses a clock, that's why the speed is called clock speed!