processor fundamentals

• A central processing unit (CPU) is a processor that processes data given by the input and then also sends this data to the output device to be shown to the user
• Characteristics of von Neumann architecture

  • CPU can access memory directly
  • Memory contains a replaceable stored program and the data required by the program
  • Program consists of individual instructions
  • CPU carries out instructions in a sequential manner
• Components of a CPU

  • Arithmetic Logic Unit (ALU)
  • Control Unit
  • Registers
• Arithmetic Logic Unit (ALU)


  Carries out arithmetic and logical operations within an active program
• Control Unit

  • Manages the data flow within the processor and throughout the entire computer system
  • Guarantees the accurate execution of instructions
• Clock


  • Internal clock controls microprocessor operation
  • System clock synchronizes the entire computer system
• Types of Registers

  • General purpose registers
  • Special purpose registers
• Accumulator (ACC)


  Stores intermediate arithmetic and logic operation results during program execution
• Index Register

  Stores indices to access specific memory locations
• Status Register (SR)


  Contains flags to indicate the outcome of various operations and conditions in the CPU
• Memory Address Register (MAR)


  Holds memory addresses
• Program Counter (PC)


  Keeps track of the address of the next instruction to be executed
• Memory Data Register (MDR)


  Stores data
• Current Instruction Register (CIR)


  Stores the instruction the CPU is currently executing
• System Bus

  • Address bus (unidirectional)
  • Data bus (bidirectional)
  • Control bus (conveys signals between control unit and other components)
• Increasing clock speed increases the number of instructions the CPU can execute per second
• Adding more CPU cores allows the processor to handle multiple tasks concurrently, improving overall system performance
• Cache

  Stores frequently accessed data and instructions from main memory, improving performance
• Word


  A fixed-size unit of data processed as a single entity by a computer, typically 16, 32, or 64 bits
• Bus width (the number of bits that can be transmitted at once) can affect system performance
• Word size


  The capabilities of a computer system in terms of the number of bits that can be processed at once
• Word length is 16 bits


  Bus width can only carry 8 bits at a time
• Bus width carrying 8 bits at a time


  A full 16-bit word needs to be transmitted in two consecutive data transfers
• Transmitting a full word in two transfers

  Affects system performance
• Factors affecting system performance

  • Clock speed
  • Number of cores
  • Cache usage
  • Bus width
• I/O

  The process of receiving data from input devices and sending data to output devices
• Device controller


  Handles the interaction between the CPU and I/O devices
• Types of ports

  • Internal ports (for integrated devices)
  • External ports (for peripheral devices)
• USB

  Allows plug and play, enables attachment of multiple devices to a single port through hubs, can manage up to 127 connected devices
• VGA port


  Offers high-quality screen display but lacks audio transmission
• HDMI


  Provides a structured and standardized way to create content with both visual and audio
• Fetch-Decode-Execute cycle

  Program counter copied to memory address register

  2. Memory data register retrieves instruction from memory address

  3. Program counter incremented (unless a jump is required)

  4. Instruction copied to current instruction register

  5. Control unit decodes and executes instruction
• Register transfer notation


  A way to precisely illustrate data flow within a computer microarchitecture
• Interrupt


  A signal or event that temporarily halts the normal execution of a program to allow the processor to handle a specific task or event, after which normal operation resumes
• Interrupt handling

  Current program state (program counter, registers) saved to memory

  2. Interrupt handler program triggered by loading its initial address into program counter

  3. After interrupt handler executed, previous program state restored from memory and normal execution resumes