What is difference between .space {value} sbrk (allocate heap memory) in MIPS

Question

in MIPS, we can allocate memory by using .space of setting $v0 to 9.

.data
arr: .space 12 # array of 12

or

li $v0, 9
li $a0, 12
syscall

I know that both will give me 12 bytes of space, sbrk allocates from heap but I actually do not know what does .space does. Can you explain is there a difference between these two?

Answer 1

Easiest way to see the difference is by looking at your compiled executable in a hex editor. When using .space n your file size has increased by n bytes. Try assembling the same program with and without the .space 12, you'll see 12 extra zeroes in the hexdump of the version with the .space 12.