First computer with real-time clock?

Tony> I don't rememebr a clock card for the '11 -- there were Tony> line-time and programmable interrupt cards that gave a periodic Tony> 'heatbeat', and that's what DEC normally regarded as a real Tony> time clock... The standard "clock" was the KW11-L -- just an interrupt tied to the mains frequency. That was a very common option in early machines and became a builtin feature of the CPU assembly in later ones. Some systems, for example those used in real time control, might have a KW11-P -- which lets you program the interrupt rate from a choice of three input oscillators (100 kHz, 10 kHz, and mains, if I remember right) along with a programmable divider. The 11/20 on which I learned in the college physics department had such a beast, and I added support for it into RT11 BASIC. There's the KW11-W, which turns out not to be the TOY clock I thought it was -- it's a watchdog. RSX systems sometimes used that. Finally, there's the KW11-C which is what I was trying to remember. That is a TOY clock. See http://www.ibiblio.org/pub/academic/computer-science/history/pdp-11/decus/1… for example. I suspect it may have been a CSS ("Computer Special Systems" -- the custom and low volume department of DEC) creation, which would be a reason for it not being well known. paul