Pentium Pro Architecture

The Pentium Pro microprocessor belongs to the CISC (Complex Instruction Set Computers) machines. Processor of Pentium Pro family are mostly present in majority of personal computers. The term ‘Pentium processor’ refers to an Intel x86 family of microprocessors that share a common architecture and instruction set.

Silent features of Pentium Pro Architecture:

  • 64 bit data bus
  • 8 bytes of data information can be transferred to and from memory in a single bus cycle
  • Supports burst read and burst write back cycles
  • Supports pipelining
  • Instruction cache

Pentium Pro Architecture:

1. Memory:
Pentium Pro microprocessor have 8-bit byte memory. Two consecutive bytes form a word, four consecutive bytes form a double word. All the address in the memory are of byte formats. Programmers usually view Pentium Pro (x86) memory as a collection of segments.

2. Register:
There are 8 general-purpose registers present in the Pentium Pro architecture. Each register is 32-bit long. First four register are used for data manipulation and next four register are used to hold address. There are some special-purpose registers in the x86 architecture such as Segment register, FLAGS register and EIP register.

3. Data Formats:

  • Integers are stored as 8-, 16-, 32-bit Binary numbers.
  • Characters are represented using 8-bit ASCII codes.
  • Floating points are represented using three different formats namely single-percision format, double-percision format, extended-percision format.

4. Instruction Formats:
All the Pentium Pro instruction uses basic format.
The basic format for Pentium Pro Instructions is:

  • Prefix: A Prefix specifies the operation of an instruction.
  • Suffix: A Suffix specifies the data type of the operands.
  • Modifier: A modifier specifies the number of operand involved.

The Opcode is the only element that is present in every instruction. Other elements may or may not present or may be of different lengths depending on the operations of instructions.

5. Addressing Modes:
Pentium Pro Architecture have a very large number of Addressing modes. Operands value is specified either by using Immediate mode or by using register mode. Operands stored in memory are specified using variation of the Target address (TA) calculation:

    TA = (base register) + (index register) * (scale factor) + displacement
  • Base register: Any general-purpose register may be used as a base register.
  • Index register: Any general-purpose register except ESP can be used as an index register.
  • Scale Factor: Scale factor may have values 1, 2, 4 or 8.
  • Displacement: Displacement may have 8-, 18-, or 32-bit values.

6. Instruction Set:
Pentium Pro Architecture has a large and complex instruction set having more than 400 different machine instructions. An instruction may have zero, one, two, or three operands. There are Register-to-Register instructions, Register-to-Memory instructions and Memory-to-Memory instructions. In Pentium Pro Architecture there are some special-purpose registers to perform operations required in the high-level programming languages.

7. Input and Output:
Input instruction transfer one byte, word or doubleword at a time from an I/O port into register EAX. Output instruction transfer one byte, word or doubleword from EAX to an I/O port. Entire string can be transferred using single operation.



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