Registers

By convention, many MIPS registers have special purpose uses. To help clarify this, SPIM defines aliases for each register that represent its purpose. The following table lists these aliases and the commonly accepted uses for the registers.

Register	Number	Usage
zero	0	Constant 0
at	1	Reserved for assembler
v0	2	Used for return values  from function calls.
v1	3
a0	4	Used to pass arguments to  procedures and functions.
a1	5
a2	6
a3	7
t0	8	Temporary (Caller-saved, need  not be saved by called procedure)
t1	9
t2	10
t3	11
t4	12
t5	13
t6	14
t7	15
s0	16	Saved temporary (Callee-saved,  called procedure must save and restore)
s1	17
s2	18
s3	19
s4	20
s5	21
s6	22
s7	23
t8	24	Temporary (Caller-saved, need not  be saved by called procedure)
t9	25
k0	26	Reserved for OS kernel
k1	27
gp	28	Pointer to global area
sp	29	Stack pointer
fp	30	Frame pointer
ra	31	Return address for function calls.