Answer from cs61c-el (David Tung 16479725) for Question 4
It means that what you type into the SPIM terminal is recorded as input to memory, and that output from memory will be displayed on the terminal.

lui $t0, 0xffff
lui $t1, 0xffff
ori $t1, $t1, 0x0004

loop: lw $t2, 0($t0)
      andi, $t2, $t2, 1
      beq $t2, $0, loop
      lbu $v0, 3($t1)