> Of course it has a clock, you can't have digital logic without a clock.
>
> Ah, then I misunderstand. =)
>
> So let me get this straight, PDP-11 gets its timing from a crystal? one of those cute
> shiny things of xxMhz, except 20 times larger in 1971?
Actually, crystals in their modern cute & shiny form were pretty much nailed down by the mid-1950s. (Pre-WW2 they were big ugly Bakelite things, but I've seen the 3.58 MHz crystals used in early NTSC color TVs and it's very recognizable to modern eyes). That said, it's possible they generated the clock on those "big iron" machines with something like the discrete-transistor version of a 555 timer rather than a crystal.
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