3. Data Organization: DB, DW, and EQU

Representing data types in assembly source files requires appropriate assembler directives.
The directives allocate data and format x86 little-endian values.
Bytes are allocated by define bytes DB.
Words are allocated by define words DW.
Both allow more than one byte or word to be allocated.
Question marks specify uninitialized data.
Strings allocate multiple bytes.
Labels in front of the directives remember offsets from the beginning of the segment which accommodates the directive.
DUP allows to allocate multiple bytes. The following two lines produce identical results:
```
    DB ?, ?, ?, ?, ?
    DB 5 DUP(?)
```
Note that EQU directive does not allocate any memory: it creates a constant value to be used by Assembler:
```
    CR EQU 13
    DB CR
    .
    mov al, CR
```

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