1.1 Systems Architecture

• Systems Architecture


  The most important part of a computer system, the CPU. Examines how modern CPUs follow instructions and how the performance of the CPU can be improved by tweaking the internal design.

  
• Embedded systems


  An important use of CPUs that are often recognised as "smart" but not necessarily a computer system.
• Central Processing Unit (CPU)


  The part of a computer system that is commonly referred to as the "brains" of a computer. Also known as the processor or microprocessor.

  
• Function of the CPU


  To fetch, decode, and execute instructions. The program code instructions are stored in the systems RAM, fetched one at a time, and retrieved along the data bus. The Control Unit decodes the instruction and sends data and signals around the CPU to carry out the instruction.

  
• Fetch Decode Execute Cycle

  1. Fetch: 1. The PC value is copied to the MAR, 2. PC is incremented, 3. The Instruction at the MAR address is read from RAM

  2. Decode: 1. The instruction in the MAR is decoded by the CU

  3. Execute: 1. The data at the MAR address is read from RAM, 2. The ALU performs any calculations required on the ACC, 3. The value in the MDR is written to the address in the MAR.

  
• John Von Neumann


  A mathematician and physicist who studied how to design a computer and came up with a system that is used almost universally in modern computer systems. His designs include the concept of having a program that is stored and is executed when the computer runs.
• Key CPU Components


  • ALU (Arithmetic Logic Unit)
  • CU (Control Unit)
  • Cache
  • Registers
  • MAR (Memory Address Register)
  • MDR (Memory Data Register)
  • Program Counter
  • Accumulator

  
• Von Neumann Architecture


  • Instructions are fetched from memory, decoded in the control unit, and then executed
  • The purpose of the CPU is to fetch, decode and execute instructions

  
• Cache


  An area of super fast memory inside the CPU chip, not unlike RAM. Can rapidly load data and code from the RAM and deliver them along the internal buses at a much faster rate compared with the external address bus and data bus.

  
• Increasing CPU clock rate

  Improves the performance of the CPU by making the whole fetch, decode, execute cycle faster
• Increasing number of CPU cores

  Improves the performance of the computer system by allowing it to carry out instructions at the same time, but only if the program had been written to make use of the extra cores

  
• Embedded systems


  Computer systems built into larger appliances or devices such as washing machines, dishwashers and microwaves. Their purpose is to monitor and control various components in the host device.
• Firmware


  The special software that controls the hardware connected to an embedded system. It is usually very basic but also very reliable.