what are the differences between data directives like .byte, .space, or .asciiz?

Question

I have seen the following directives but I don't know exactly the usage:

1. .space
2. .byte
3. .word
4. .asciiz
5. .ascii
6. .align

Answer 1

1. .space reserves n bytes of memory, without aligning. e.g. arr: .space 100
2. .byte store the n values in successive bytes of memory. e.g. num: .byte 0x01, 0x03
3. .word store n 32-bit words contiguously in aligned memory. e.g. val: .word 10, -14, 30
4. .asciiz stores string in memory with a null terminator. e.g. str: .asciiz "Hello, world"
   Exactly like .ascii with a .byte 0 after it.
5. .ascii stores string in memory without a null terminator. e.g. str: .ascii "Hello, world"
6. .align aligns the next data on a 2^n byte boundary. e.g. .align 2 aligns the next value on a word boundary. On the other hand if n is 0 then alignment is turned off until next data segment.

For a detailed information see this assembly reference.

For more details about .align, see

• Understanding Assembly MIPS .ALIGN and Memory Addressing
• MARS MIPS simulator's built-in assembler aligns more than requested? - .align in classic MIPS assemblers (like MARS) works differently from modern GAS and clang: in classic MIPS assemblers, it can put padding before an earlier label, instead of expanding to padding wherever you put it. (.word and .half also align an earlier label, unlike .space)