Register Mnemonics

Although the registers are called "general purpose", it is conventional in software to use each register for a specific purpose. This is not required by hardware. It is just a way for programmers to avoid confusion by establishing conventions. The extended assembler uses mnenomic names for registers that show how they are used.

For example, registers $8 through $15 are conventionally used to hold temporary values. The mnemonic name for these registers is $t0 through $t7.

Register Number	Mnemonic Name	Conventional Use		Register Number	Mnemonic Name	Conventional Use
$0	$zero	Permanently 0		$24, $25	$t8, $t9	Temporary
$1	$at	Assembler Temporary		$26, $27	$k0, $k1	Kernel
$2, $3	$v0, $v1	Value returned by a subroutine		$28	$gp	Global Pointer
$4-$7	$a0-$a3	Subroutine Arguments		$29	$sp	Stack Pointer
$8-$15	$t0-$t7	Temporary		$30	$fp	Frame Pointer
$16-$23	$s0-$s7	Saved registers		$31	$ra	Return Address

As far as hardware is concerned, only registers $0 and $31 are different from the rest ($0 is always full of zeros and $31 is automatically used by some subroutine linkage instructions to hold the return address). The remaining registers are electronically identical. It is a software convention to use different sets of registers for different purposes.