The bit pattern in
$8 is moved to
$8 is unchanged).
or $9,$8,$0 # $9 <— contents of $8.
Copying the pattern in a source register to a destination register is called a move operation, even though the source register does not change.
or d,s,$0 # $d <— contents of $s.
(Review:) How can a particular bit pattern be loaded into a register?