64 - Bit Processor Notes | Study Digital Electronics - Electronics and Communication Engineering (ECE)

64 – bit Processor

• 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 performed.
• The various function performed by the microprocessor can be classified as:
  • Microprocessor initiated operations
  • Internal operations
  • Peripheral operations
• Microprocessor initiated operations mainly deal with memory and I/O read and write operations.
• Internal operations determines how and what operations can be performed with the data.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 speci al operations like reset, interrupt, ready, etc.
• The block diagram of 64-bit microprocessor is shown below.
• The major parts of the block diagram are:
  • General register unit
  • Control and decoding unit
  • Bus unit o Cache memory unit
  • Floating point register unit
  • Issue ports

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 environment. i.e 24,32 or 64 bit mode
• PSW bits 31 and 32 designate addressing mode (out of 64 bit).
  • 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:
  •  Address generation in 64-bit mode.

• The register is treated as 32-bits for:
  •  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: