The course work of Operation System
$0 always zero
$1 $at assembly reserved register
$2-3 $v0-1 syscall id & return value
$4 $a0 syscall argument
$5 void
$6-9 add & sub register (%eax)
$10-13 base register (%ebx)
$14-17 counter register (%ecx)
$18-21 modula register (%edx)
$22-23 (%esi)
$24-25 (%edi)
$28 manual stack point (use for push & pop)
$29 stack point (%esp)
$30 frame point (%ebp)
$31 return address register