• The brain of the PC is processor or CPU.
  • It performs the system’s calculating and processing Operations.
  • The term N-bits means that its ALU, internal registers and most of its instructions are designed to work with N-bit binary words.
  • The major components of CPU are:


  • 64-bit processors have 64-bit ALUs, 64-bit registers, and 64-bit buses.
  • A 64-bit register can address up to 264 bytes of logical address.
  • 64-bit processors have been with us since 1992.
  • Eg: 64-bit AMD processor.


Internal Architecture

  • The internal logic design of microprocessor which determines how and when various operations are
  • The various function performed by the microprocessor can be classified as:
  1.  Microprocessor initiated operations
  2. Internal operations
  3. Peripheral operations
    • Microprocessor initiated operations mainly deal with memory and I/O read and write
    • Internal operations determines how and what operations can be performed with the The operations include:
  1. storing
  2. performing arithmetic and logical operations
  3. test for conditions
  4. store in the stack
  • External initiated operations are initiated by the external devices  to perform special operations like reset, interrupt, ready,
  • The block diagram of 64-bit microprocessor is shown
  • The major parts of the block diagram are:
  1. General register unit
  2. Control and decoding unit
  3. Bus unit
  4. Cache memory unit
  5. Floating point register unit
  6. Issue ports

                       Fig: Block diagram of 64-bit internal architecture

Architecture Elements

  • Addressing Modes
  • General Purpose Registers
  • Non-modal and modal Instructions
  • New Instructions in Support of 64-bit
  • New immediate Instructions

Addressing modes

  • This addressing mode determines the working i.e 24,32 or 64 bit mode
  • PSW bits 31 and 32 designate addressing mode (out of 64 bit).

             o Addressing modes bits:00=24 bit-mode

                 01=32 bit-mode

                11=64 bit-mode

General purposes register (GPR)

  • The register is treated as 64-bits for:

o Address generation in 64-bit mode.

  • The register is treated as 32-bits for:

           o Address generation in 24/32-bit mode.

New instructions in 64-bit:

  • Load Reversed - LRV, LRVR
  • Multiply Logical - ML, MLR
  • Divide Logical - DL, DLR
  • Add Logical w/ Carry - ALC
  • Subtract Logical w/ Borrow - SLB
  • Store Reversed - STRV
  • Rotate Left Single Logical – RLL

New immediate Instructions

  • Load Logical Immediate
  • Insert Logical Immediate
  • AND Immediate
  • OR Immediate
  • Test Under Mask (High/Low)

Comparison of 64-bit with 32-bit

  • Contains 32-bit data lines whereas 64-bit contains 64 data lines.
  • Can address max 2^32(4 GB) of data whereas 64 bit can address 2^64(18 billion GB).
  • Speed and execution is both fast in 64-bit processors.
  • 64-bit processors can drive 32-bit applications even faster, by handling more data per clock cycle than a 32-bit processor.
  • The table shows the basic difference between two: