Path: utzoo!attcan!uunet!husc6!bloom-beacon!mit-eddie!uw-beaver!tektronix!tekcrl!tekgvs!toma
From: toma@tekgvs.GVS.TEK.COM (Tom Almy)
Newsgroups: comp.misc
Subject: Re: computer follies
Message-ID: <4041@tekgvs.GVS.TEK.COM>
Date: 6 Oct 88 14:16:15 GMT
References: <916@viscous> <1086@bucket.UUCP> <23134@amdcad.AMD.COM>
Reply-To: toma@tekgvs.GVS.TEK.COM (Tom Almy)
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 31

In article <23134@amdcad.AMD.COM> rpw3@amdcad.UUCP (Rob Warnock) writes:
>
>On PDP-11's with real core (not this modern RAM stuff!), there was a
>power-fail interrupt that gave you enough time to save critical state
>and go into a loop before the CPU quit working. It you diddled things
>right, you could take the power-on interrupt and restore your state and
>continue where you left off. In particular, the FOCAL/F interpreter
>contained the needed code,.

BASIC also did this.  I was once running a several hour long BASIC program
when the power failed.  Sure enough, when power was restored, the program
continued to successful completion.  

I'd sure like to see systems do that these days!  (Especially a *NIX system!).

The system bootstrap code was contained in a ROM that consisted of a diode
matrix on a circuit board.  To boot the system from the halt state you would
set the address of the rom in the switches, press load address, and then put
the address of the boot device in the switches and put the run/stop switch in 
run.  Since I had only one boot device, I moved some diodes around so that
the device address was a literal instead of being read from the switches.
Then I patched the system so that the power-fail interrupt was vectored to
the bootstrap rom.  Now when I turned the system off it would pfi to the
boot routine, where it would be to reboot the system when power was
restored!  This gave me convenient operation much like todays personal
computers.  (Of course, If I ran basic, I needed to hit load address and run
because the vector would have been changed...).

Tom Almy
toma@tekgvs.TEK.COM
Standard Disclaimers Apply