Intel Assembly Addressing Mode

Global variable is defined in a .DATA section. DB, DW and DD declare variables of 1, 2 and 4 bytes in length.

.DATA
var1 DB 64 ; initialize variable with value 64
var2 DB ? ; uninintialized variable
var3 DD 1, 2, 3 ; declare 3 doubleword variables and initialized to value 1, 2 and 3

arr1 DD 100 DUP (0) ; declare and array of 100 entries. Initialized to 0
str1 DB 'hello',0 ; declare a null terminating string of 6-bytes long

mov eax, [ebx] ; move the eax content to 4 byte pointed to by address in ebx
mov [eax], ebx ; move the ebx content to the address stored in eax

Somtimes, the size of data during manipulation is ambiguous e.g. when immediate value is used

mov BYTE PTR [ebx], 2 ; move 2 into a single byte at address stored in ebx
mov WORD PTR [ebx], 2
mov DWORD PTR [ebx], 2