Q:

Assembler: jmpf, testb and else instructions

Help me please, i don't understand this code:
...
BUFFER = 0x0600
...
rep movs jmpf BUFFER+migrate, 0 ;??? 
migrate:
findactive:
testb dl,dl ; ??? 
jns nextdisk

A:

I'm an old x86 coder.    I have to admit I don't understand your code either. 
The "movs" instruction line looks illegal.    Are you sure you've transcribed the code correctly?