58 THE x86 MICROPROCESSORS
fl ag (DF) is used in string operations. Details of the functioning of these fl ags will be discussed
in later chapters.
Arithmetic Logic Unit It is the part of a computer that performs all arithmetic and logic
computations. e ALU is the most important unit of the processor. Instructions that are
fetched and decoded, are executed in the ALU. us the ALU has direct access to the general-
purpose registers and fl ags.
1.3 | Bus Interface Unit
is unit is responsible for address calculations, pre-fetching instructions for the queue and
sequencing instructions one by one. Let us examine each function.
1.3.1 | The Instruction Queue
Instructions are found in memory, from where they are fetched and decoded as and when ...