====== Data Types and Encoding ======
===== Fundamental data types =====
Fundamental data types cover the types of data elements that are stored in memory as 8-bit (Byte), 16-bit (Word), 32-bit (Doubleword), 64-bit (Quadword) or 128-bit (Double quadword), as shown in figure {{ref>fundamentaldata}}. Many instructions allow for processing data of these types without special interpretation. It depends on the programming engineer how to interpret the inputs and results of instruction execution. The order of bytes in the data types containing more than a single byte is little-endian. The lower (least significant) byte is stored at the lower address of the data. It represents the address of the data as a whole.

The data types which can be used in the x64 architecture processors can be integers or floating point numbers. Integers are processed by the main CPU as single values (scalars). They can also be packed into vectors and processed with the specific SIMD instructions, including MMX and partially by SSE and AVX instructions. Integers can be interpreted as unsigned or signed. They can also represent the pointer to some variable or address within the code. Real numbers are processed by the FPU as scalars. SSE and AVX instructions support calculations with scalars or vectors composed of real values. All possible variants of data types are stored within the fundamental data types. Further in this chapter, we describe all possible singular or packed integers and floating-point values.

<figure fundamentaldata>
{{ :en:multiasm:cs:fundamental_data_types.png?800 |Illustration of fundamental data types}}
<caption>Fundamental data types</caption>
</figure>

===== Integers =====
Integers are the numbers without the fractional part. In x64 architecture, it is possible to define a variety of data of different sizes, all of them based on bytes. A single byte forms the smallest possible information item stored in memory. Even if not all bits are effectively used, the smallest element which can be stored is a byte. Two bytes form the Word. It means that in x64 architecture, Word data type means 16 bits. Two words form the Double Word data type (32 bits), and four words form the Quad Word (64 bits). With the use of large registers in modern processors, it is possible to use in a few instructions the Double Quad Word data type, containing 128 bits (sometimes called Octal Word).

===== Floating point values =====