1.1 Systems Architecture

• Fetch


  The action of collecting the instructions from the memory
• Execute


  The action of the CPU carrying out the action
• Decode


  Making sense of the instruction
• Types of memory


  RAM and ROM
• What does RAM stand for?

  Random Access Memory
• What does ROM stand for?

  Read Only Memory
• What does the CPU stand for?

  Central Processing Unit
• What does the CPU do?


  Takes in data then processes it and delivers an output
• What is considered the brain of the computer?

  CPU
• What performs the fetch-decode-execute?

  CPU
• How many times is the fetch-decode-execute performed per second?

  Billions
• What happens at the fetch stage?


  The instructions are fetched from RAM and brought back to the CPU
• What happens at the decode stage?

  The instructions are inspected and figured out what needs to be done with them
• What happens at the execute stage?


  The CPU carries out the instructions on the data this could be actions like:

  - Going back to main memory and grabbing some data

  - Performing some calculations

  - Storing information back into the main memory
• Clock speed


  Dictates how many instructions the CPU can process each second
• Clock speed: 3Ghz processor

  3 billion cycles per second
• What does the Arithmetic Logic Unit (ALU) do?


  - Arithmetic calculations

  - Making logical decisions
• What is the Control Unit?


  This is the control centre of the CPU. It sends signals to control how the data moves around the CPU.
• Cache


  This a very small piece of memory. It provides fast access to frequently used instructions and data.
• What are registers?


  Tiny, super fast pieces of onboard memory inside the CPU each with a very specific purpose
• What are the 4 registers?

  - The accumulator

  - The Program Counter

  - The Memory Address Register

  - The Memory Data Register
• Register


  A small amount of fast storage in the CPU
• CPU Architecture


  The design of the CPU (how it has been constructed)
• Accumulator


  A specialised CPU registered which stores the immediate results of the F-D-E cycle
• What are the main types of architecture?


  - Von Neumann architecture

  - Harvard architecture
• What are modern day CPUs called?

  Von Neumann architecture CPU
• What is the main memory called?

  RAM
• What is in the Von Neumann architecture?


  - Control Unit(CU)

  - Algorithmic Logic Unit(ALU)

  - Memory unit (typically RAM)

  - Input and Output
• Program Counter (PC)


  holds the address of the next instruction to be executed
• Memory Address Register (MAR)


  Holds the address in memory of the instruction at present being executed.
• Memory Data Register (MDR)


  Holds the data fetched from, or to be written to memory
• What is clock speed?


  - Measured in Hertz (Hz)

  - Number of fetch-decode-execute cycles per second

  - Modern processors operate at billions of cycles per second, GigaHertz GHz

  - 3.2 GHz clock speed = 3.2 billion instructions can be fetched per second

  - This whole cycle is controlled by the Control Unit on the CPU and clock

  - The faster the clock tick the quicker it can perform a cycle
• What is overclocking?


  When the clock is faster then the CPU can perform the calculations to perform faster
• Why is overclocking dangerous?


  The issue is that CPUs get very hot so overclocking can be dangerous if you don't manage the heat properly
• What is the cache size?


  - Cache is a temporary storage of data and instructions being read and written from

  - Located on the board or very close to the CPU

  - Stores copies of recent data and instructions

  - Much quicker then getting items from RAM

  - Trying to avoid going and getting instructions and data from memory if we don't need it as it cost time

  - The more instructions and data that can be stored in cache, the more efficient the CPU is
• Why do we still need main memory if we have cache?


  Because the cache is vey small
• Number of cores


  - A core is a complete copy of ten CPU

  - So a quad-core processor would have 4 separate processing units each with its own:

  . Register

  . ALU

  . Accumulator

  . CU

  - Doubling the number of cores won't simply double the overall speed

  - CPU cores have to communicate with each other, which takes time

  - Many programs are not designed to make use of multiple cores
• Process


  The action taken by a computer
• Embedded


  Something that is implanted
• CPU cores


  An independent processing unit that is able to fetch, decode and execute instructions