On Sun, 1 Aug 2004, Tom Jennings wrote:
> On Thu, 2004-07-29 at 13:20, Vintage Computer Festival wrote:
>
> > I'm more interested in a clock/calendar: something that could be polled
> > and produce the local time and date.
>
> But but... this isn't an obvious statement, even... even 'stand-alone
> battery-backed chips producing BCD date & time in English' require
> interpretation (interface protocol, output, etc) schematically no
> different than the simplest timer tick, via interrupt or mainline code
> IO or memory poll (or hell HALT). Then there's light-to-dark-grey chips
> that produce isochronous events, even timedate specific, in all sorts of
> intermediate forms, seconds since FOO, etc. Every hardware programmer
> has coded dozens. I did one/many for CP/M (in my homemade command
> interpreter) and MSDOS, etc.
Hmm, okay. Then I guess what we'd be looking for is some device that
keeps continuous time. I.E. you set it once, and through some manner of
both hardware and software, produces the correct current date and time
upon request.
As far as need to keep the time during power off, I don't know that in
this case it would matter too much. It would just have to be a
combination of hardware and software that kept the current date in the IBM
650. The 650 was small enough that you could power it down during off
hours, though I don't know what actual practice was (perhaps it was too
much of a chore to boot up so it was kept on all the time). At any rate,
as long as the 650 had some way to generate uniform time pulses, a
real-time clock/calendar could be implemented, but this would probably
have to be at a hardware level since the 650 was primarily a batch
machine, or it would have to be programmed to store the date/time in some
memory location that the other applications would not touch, and then some
counter would have to be implemented that could update a memory location
with the number of ticks since the last access or whatever.
Of course, as I've been suggesting, there could have been a totally
separate clock/calendar device (heck it could have even been mechanical)
that kept the local time/date and then transferred it to the 650 upon
request. Just like the clock in a modern PC.
> My favorite on the opposite end, is a random bit stream produced by
> using the pulses from a geiger counter (and associated radioactive
> material) to clock a long shift register. It's well-discussed, but I'm
> not sure anyone ever produced one.
How fun. You'd have to shield it pretty heavily though or else your PC
would be glowing at night (talk about a case mod!)
Has anyone ever produced a random number generator that pulls it's "seed"
from the random background radiation you get on a TV set on a dead channel
(snow)?
--
Sellam Ismail Vintage Computer Festival
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Received on Sun Aug 01 2004 - 17:32:25 BST