🚀 go-pugleaf

 bob@reed.edu (Robert Ankeney) writes:
>     One thing I was just remembering was a wonderful puzzle from way
>back when.  It was a challenge to write a program that zeroed memory.
>It had to be written in the first 4K and would zero the entire 4K,
>including itself.  So, if you're feeling bored, you might see if you
>can do it!  Sadly, I don't remember any solution, but if I recall,
>the auto-increment registers at 10-17 might have been useful.

A puzzle?  We ran this little ditty on almost a daily basis.
0000 ADDR LD
DCA I 0010
JMP 0000
0000 ADDR LD CLEAR CONT

2 instructions.  Actually, we'd run it with the data field set to 1,
then 2, and finally zero.  The program autoincrements itself right
through the field, finally (in DF0) overwriting the DCA with a zero.
(AND 0000)  Then the loop was a lot tighter -- you could see the
difference in the panel lights.  You do have to make sure that
location 10 has a 10 in it when you start, though...

Why did this get run so often?  Because the teachers didn't know how
to reload BASIC, so if the machine went down they'd have to corral a
convenient student, write him a pass out of his next class, and "make"
him reload it.  If you didn't have a panel key, this program would
bring EDUSYSTEM-20 to its knees:
10 DEF FNA(X)=FNB(X)
20 DEF FNB(X)=FNA(X)
30 PRI FNA(1)
RUN
<CRUNCH>

Another interesting pdp8 trick:  Since we had (4) ASR-33s as our only
IO, we wrote a "fourple loader" which would read a clunk from each TTY
in turn.  (The first character was on tape 1, the second on tape 2,
etc.)  This ended up being almost 4 times as fast as loading
through 1 TTY, since most of the time was spent just waiting for the
reader to come ready again.  Each TTY used a tape with a different
leader character, and the loader would figure out which tape was in
which TTY.  Nowadays I think they call this "reverse multiplexing."

-- 
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Gordon S. Hlavenka           cgordon@vpnet.chi.il.us
Vote straight ticket Procrastination party Dec. 3rd!