Not too hard to memorize zero.
0 0 0 0 0 0 0 0 -- machine instruction in hex 0000 0000 0000 0000 0000 0000 0000 0000 -- machine instruction in bits 000000 00000 00000 00000 00000 000000 -- fields of the instruction opcode ----- $0 $0 0 2ndary -- meaning of the fields sll source dest shft sll
Register
$0 always contains a 32-bit zero (have you heard this before?) so
shifting it left by zero positions and attempting to put the result
back in $0 does nothing.
Any instruction that attempts to alter $0 does nothing,
but this instruction is the preferred way of doing nothing.
A machine instruction that does nothing is called (in official computer science jargon) a no-op. The no operation instruction is surprisingly useful, especially for MIPS.
What do you call a human who does nothing?