doing pcb/task_struct leads to changes in/with:

CPU structure.
SCH structure.
Interrupt/IPLs. Interrupt stack. iret/REI & ASTs.
Syscalls: copied linux ones and use 0x81.
	  VMS does not seem to use interrupt for syscalls at first, a bit later
Memory management: need to be studied

Currently broken:
MD support
SMP support
