Computer science System architecture 1.1

• Central Processing Unit (CPU)


  The brain of a computer, responsible for executing instructions and performing calculations
• Key components of the CPU

  • Control Unit (CU)
  • Arithmetic Logic Unit (ALU)
  • Registers
  • Memory Unit (MU)
• Control Unit (CU)


  The "conductor" of the CPU, fetching instructions from memory, decoding them, and directing the execution process
• Arithmetic Logic Unit (ALU)


  Performs arithmetic and logical operations, such as addition, subtraction, multiplication, and comparison
• Registers


  Small, high-speed memory units that temporarily store data and instructions during processing
• Memory Unit (MU)


  The main storage unit of the CPU, holding instructions and data that the CPU needs to access
• Fetch-Decode-Execute (FDE) Cycle


  1. Fetch: The CU retrieves the next instruction from memory

  2. Decode: The CU analyzes the instruction, determining what operation to perform and what data to use

  3. Execute: The ALU performs the specified operation using the decoded data, producing the result
• Factors Affecting CPU Performance

  • Clock Speed: The number of instructions a CPU can execute per second
  • Number of Cores: A CPU core is a processing unit that can execute instructions independently
  • Cache: A small, high-speed memory that stores recently used data and instructions, reducing the need to access slower main memory
• Embedded Systems


  Specialised computers designed to perform specific tasks within a larger device or system
• Key Characteristics of Embedded Systems

  • Tightly Coupled Hardware and Software
  • Real-Time Constraints
  • Limited Resources
  • Reliability and Robustness
• Frequent and common mistakes made in paper 1
• CPU

  Central Processing Unit
• The CPU fetches and decodes instructions
• The speed of a CPU is usually measured in GigaHertz (GHz)
• Registers inside the CPU

  • MAR (memory address register)
  • MDR (memory data register)
• Cache size

  Affects the performance of the CPU by storing the data and instructions currently required by the CPU, reducing the need to access slower RAM
• Fetch-execute cycle

  1. Memory address register copies the address of the next instructions in the RAM

  2. Memory data register stores the data from the RAM which will be decoded

  3. Program counter increments by 1

  4. ALU performs the logical calculation

  5. Instruction is fetched from memory

  6. Instruction is then decoded

  7. Decoded instruction is then executed

  8. Process is repeated

  9. Program counter is incremented

  10. Instruction is transferred to the MDR

  11. Address of the instruction to be fetched is placed in the MAR
• Dual core processor

  • Instructions can be decoded faster as cores can work collectively or separately on different tasks
  • Allows for multitasking to take place
• Embedded system

  An electrical system that is part of a larger electronic system and performs one particular task
• Devices containing embedded systems

  • Dishwasher
  • Microwave
  • Cruise control systems in cars