General register list (applies to MIPS ISA and project)
                      (note: project op codes may differ from MIPS/SGI)

Register          notes
 0   $0           zero value, not writable
 1   $1
 2   $2   $v0     return values (convention, not constrained by hardware)
 3   $3   $v1
 4   $4   $a0     arguments (convention, not constrained by hardware)
 5   $5   $a1
 6   $6   $a2
 7   $7   $a3
 8   $8   $t0     temporaries(not saved by software convention over calls)
 9   $9   $t1
10   $10  $t2
11   $11  $t3
12   $12  $t4
13   $13  $t5
14   $14  $t6
15   $15  $t7
16   $16  $s0     saved by software convention over calls
17   $17  $s1
18   $18  $s2
19   $19  $s3
20   $20  $s4
21   $21  $s5
22   $22  $s6
23   $23  $s7
24   $24  $t8     more temporaries
25   $25  $t9
26   $26  
27   $27  
28   $28  $gp     global pointer ( more designations by software convention)
29   $29  $sp     stack pointer
30   $30  $fp     frame pointer
31   $31  $ra     return address

Remember: From a hardware view registers 1 through 31 are general purpose
and identical. The above table is just software conventions.