Weak sectors on CDs

Here is a very good explanation of the weak sector problem on CDs:
http://ixbtlabs.com/articles2/magia-chisel/. It is used in some copy protection schemes like SafeDisc. It reminded me of weak data I produced on the C64 where GCR-encoding  was done in software. So you could easily write something that is not well formed. Doing this led to sectors that contained different data every time you read them. Very funny. And confused every copy program I know of.

Blitter kills

The Amiga was an absolutely marvellous  machine. It had so fantastic special hardware for that time. It was incredible. Two of them where Copper and Blitter. A funny trick to hinder the debugger was to set up the Copper to tell Blitter to fill the memory of your running program with 0x00 the next time the cathode ray reaches a specific position. Your program regularly stopped the Copper from doing this. But if you stopped the CPU with a debugger, Copper and Blitter continue there work and killed your programm or other important things.

Early warnings

Once upon the time I was browsing through a book which disassembled the Amiga Kickstart-ROM (well I don't remember it's name but it was long before the very nice Amiga Guru-Buch came out). What I saw there, immediately caught my  attention. If the filesystem on a new mounted filesystem had a specific problem it would try to load a program to fix it. The interesting point was, that it first tried to load from that filesystem! If it couldn't find it there it tried the system-partition. Some hours later I had a floppy that upon inserting it into your Amiga immediately showed a very nice custom Guru-Meditation. I showed this floppy to a friend of mine who was astonished as well because the Amiga had no known feature to automatically start a program upon inserting a floppy. It was very hard to keep it from starting it. Luckily viruses where more a theoretic thing at that time. We had copy protection on our mind. It would be very funny to start the game immediately upon inserting the disk.

WX

I just remember that the Motorola 68000 build into the ATARI-ST had a very small cache. It could be used for a funny trick to hinder the debugger. If you just wrote the next instruction with a move the 68000 executes the instruction that was there before. But if you used a debugger you would execute the new instruction. Obviously you had to make sure that no interrupts occurred.