1.1 - System architecture

• System architecture


  The arrangement and interconnection of the components that make up a computer system
• CPU


  • The purpose of the CPU is to process data, carry out instructions and control the components of the computer
  • The CPU is made up of billions of transistors that create logic circuits
• Fetch-Execute cycle


  1. Fetch instructions from memory

  2. Decode instructions

  3. Execute instructions
• Arithmetic Logic Unit (ALU)


  Responsible for arithmetic operations (add, subtract, multiply, divide) and logical operations (AND, OR, NOT, comparisons)
• Control unit (CU)


  Coordinates the activity of the CPU by fetching and decoding instructions, and sending signals to control the movement of data
• Cache memory


  Provides temporary storage that the CPU can access very quickly to store instructions and data that are used repeatedly or likely to be required
• Registers


  Memory locations within the CPU that hold data temporarily and can be accessed very quickly
• Von Neumann architecture


  • CPU architecture where data and instructions are stored in the same area of memory and are indistinguishable from each other
  • Important registers: Program Counter, Memory Data Register, Memory Address Register, Accumulator
• Fetch-Execute cycle in Von Neumann architecture

  Copy address of next instruction from Program Counter to Memory Address Register

  2. Fetch data stored at that address to Memory Data Register

  3. Increment Program Counter

  4. Decode instruction in Memory Data Register

  5. Execute decoded instruction
• Clock speed


  The speed at which the CPU fetches and executes instructions, measured in hertz (Hz)
• Cache memory size


  Larger cache memory means more data can be stored and accessed quickly, improving CPU performance
• Number of processor cores

  Multiple cores can handle several instructions at the same time, improving performance if the program is designed to take advantage of it
• A quad core processor has four processor cores
• 2.3 GHz CPU


  The CPU can execute 2.3 billion instructions per second
• Characteristics affecting CPU performance

  • Clock speed
  • Cache memory size
  • Number of processor cores
• Embedded system


  A computer system designed to perform a dedicated function, often with real-time computing constraints
• Cache memory


  • Sits between the processor and main memory (RAM)
  • The CPU looks in the cache for required data
  • If it is not there, it requests it from RAM
  • The data is moved into cache before being accessed by the CPU
• Registers


  • Memory locations within the CPU that hold data
  • A register may hold an instruction, a storage address or any kind of data
  • The data in registers can be accessed very quickly – even more quickly than cache memory
• Von Neumann architecture


  • CPU architecture refers to the internal logical structure and organisation of the computer hardware
  • Data and instructions are stored in the same memory
  • Program counter (PC): Stores the address of the next instruction to be processed
  • Memory data register (MDR): Stores data fetched from memory or to be sent to memory
  • Memory address register (MAR): Stores the address of the location in memory for data to be fetched from or sent to
  • Accumulator (ACC): Stores the results of any calculations carried out by the ALU
• CPU performance


  • Clock speed: The faster the clock the more instructions that can be completed per second
  • Cache memory: Having more cache will provide the CPU with fast access to more data
  • Number of cores: If a CPU has multiple cores it may be able to process more instructions simultaneously
• Embedded system


  • A computer system that has been designed for a dedicated function as part of a bigger system
  • Often manufactured as a single chip
  • The dedicated hardware and software make embedded systems more robust and reliable than general-purpose computers
• Characteristics of embedded systems

  • Designed and engineered to perform a limited set of tasks to reduce size and improve performance
  • Programs are often uploaded at the manufacturing stage, directly to the device
  • There are often very limited options to modify these programs
  • Low power consumption to operate from a small power source
  • Small in size to fit in portable devices
  • Rugged so that they can operate in hostile environments
  • Low cost making them suitable for mass-produced products
• Examples of embedded systems

  • Washing machines
  • Microwave ovens
  • Home security systems
  • Home heating controls
  • Car engine management systems
  • Set-top boxes
  • Telephones
  • Televisions
  • Home security and control systems