What is the difference between the sets of MIPS codes?

Question

What is the difference between two codes?

.data            |  .data
A:  .word   0:100|  A:  .word   0:100
                 |
.text            |  .text
li  $t1, 4       |  la  $t1, A
lw  $t0, A($t1)  | lw    $t0, 4($t1)

Answer 1

Lets understand the code line-by-line:

Right:

    .data         # static variables are defined in .data block
A:  .word   0:100 # array 100 of integers each initialized to 0 

    .text         # MIPS code block
li  $t1, 4        # loading a 16 bit constant value 4 into register $t1

lw  $t0, A($t1)   # going to the memory at the address of A (address
                  # of first element of array) + $t1 (which contains
                  # value 4) and fetch it into register $t0

Left:

    .data         # static variables are defined in .data block
A:  .word   0:100 # array 100 of integers each initialized to 0 

    .text         # MIPS code block
la  $t1, A        # load the address of first element of array 
                  # into register $t1

lw $t0, 4($t1)    # going to the memory at the address of $t1 + 4 
                  # and fetch it into register $t0

Notes: Addresses in MIPS are in bytes and integers (.word) are 4 bytes. Hence, if we increment base addresses of array (base address of array) by 4, it will result in address of second element of array.

Therefore: The two codes are identical. In the end, content of second element of array (at index = 1) will be loaded into register $t0.