MIPS sb operator: other 3 bytes

Question

sb $s. i($d)

When the least significant byte of $s is stored at memory address [i+$d], what is the other 3 more significant bytes of [i+$d]?

Is it the sign-extension or zero-extension of the least significant byte at $s?

Edit: sb stores the least significant byte of $s into exactly 1 byte of space at address [i+$d]. Thus, no extension is required.

Answer 1

sb is Store Byte - nothing is stored at any other address.