A long time ago i took a book about doing funny stuff in dos, and wrote own additions in the sidelines of the book. Or used the empty pages.

It contains jokes using autoexec.bat and config.sys. Additions by me are most of the time things you could do with debug.com, a little program which existed on any pc at that time.

A little program which created static on a CGA or Hercules monitor. Yes, that long ago. CGA provided 16 colors in 80×25 or 40×25 text modes, but only four colors at 320×200 resolution and two colors at 640×200. Hercules was only monochrome and a max resolution of 720×348. It was on a hercules card i made my first copperbar. ( Before the effect was named copperbar ). Due to difference in timing on every machine, you had to get the copperbar timing right by using two keys i’d assigned the timing to.

MOV AL,00                      # Fill AL register with 0
MOV DX,0x03D8 (cga) 03B8 (herc)# DX with address
OUT DX,AL                      # Set address with AL
MOV AL,[0101]                  # Reg AL with contents 
INC AL                         # Increment AL
MOV [0101],AL                  # Address fill with AL
JMP 100                        # Jump to start

The opcodes for the program :

b0 00
66 ba d8 03
ee
a0 41 00 00 00  
fe c0
a2 41 00 00 00 
e9 60 00 00 00

Sometimes i put these little programs in autoexec.bat, so at next restart of the pc, it would do something weird. My little BOFH jokes. Friends and computerstores where not safe.

Another example:

Two drives in a PC ? (Wie A: zegt moet ook B: zeggen)
Use with care, below will f*ck up your drives. (And makes a lot of noise while doing so.)

MOV DX,0x03F2
MOV AL,71
OUT DX,AL
MOV AL,74
OUT DX,AL
JMP 100

( https://en.wikipedia.org/wiki/Floppy-disk_controller )