This is the shortest program I have ever written and expected to do something:
I wrote that on a timesharing host in the eighties. The host had a Z80 processor and ran MP/M (a multiuser variant of CP/M), and I was curious to see whether my code would affect other users. The host did not have an assembler, but I knew the bit patterns for most assembly instructions by heart anyway.
I did one thing right: I didn't tell anyone in advance. Never ask a question if you already know what the answer will be. Instead I waited until just before the end of the class.
And I did two things wrong. What I wanted was
di ; disable interrupts
halt ; stop processing until interrupted
Sadly, halt is 118 and di is 243, which was my first mistake. And
the second was that when it didn't work, I told someone (
were you doing there at the end, Arnt?), which led to a ban on
such experiments before I had found the first mistake.