Systems architecture

• General purpose computer


  A computer designed to be able to carry out a wide range of instructions
• Examples of general purpose computers

  • PC
  • Tablet
  • Smartphone
  • Games console
  • Media system in car
• Hardware


  The physical components of a computer system, e.g. CPU, hard disk drive, monitor
• Software


  The programs that run on a computer
• General purpose computer model

  1. Data input

  2. Data processed by CPU

  3. Results output or sent to secondary storage
• CPU


  The most important hardware component in a computer, processes data/instructions and controls the computer system
• The purpose of the CPU is to process data and instructions, and to control the rest of the computer system
• Fetch-decode-execute cycle


  How a processor functions
• Fetch-decode-execute cycle


  1. Memory address held in program counter copied into MAR

  2. Program counter incremented by 1

  3. Processor sends signal along address bus to memory address in MAR

  4. Instruction/data held in that memory address sent along data bus to MDR

  5. Instruction/data held in MDR copied into CIR

  6. Instruction/data held in CIR decoded and executed

  7. Results stored in ACC

  8. Cycle returns to step 1
• Additional steps may be taken depending on the type of instruction
• Additional steps for instruction to transfer data from ACC to primary memory

  1. Memory address copied into MAR

  2. Data to be transferred copied into MDR

  3. Data transferred to specified address using address bus and data bus
• Additional steps if executed instruction requires program to jump to different place

  1. Memory address of new next instruction copied into program counter

  2. Process restarts at step 1
• Von Neumann architecture provides the basis for the majority of the computers we use today
• The fetch-decode-execute cycle describes how a processor functions
• Von Neumann architecture


  Provides the basis for the majority of the computers we use today
• Fetch-decode-execute cycle


  Describes how a processor functions
• Common CPU components


  • Control unit (CU)
  • Arithmetic logic unit (ALU)
  • Registers
  • Cache memory
  • Buses
  • Clock
• Control unit (CU)


  • Fetches, decodes and executes instructions
  • Issues control signals that control hardware
  • Moves data around the system
• Arithmetic logic unit (ALU)


  • Performs arithmetic and logical operations
  • Acts as a gateway between primary memory and secondary storage
• Cache


  • Small amount of high-speed random access memory (RAM) built directly within the processor
  • Used to temporarily hold data and instructions that the processor is likely to reuse
• Registers


  • Program counter
  • Memory address register (MAR)
  • Memory data register (MDR)
  • Current instruction register (CIR)
  • Accumulator (ACC)
• All components work together to allow processing and system control
• Name the parts in Von Neumann Architecture below:

  A) RAM

  B) CPU

  C) Secondary Storage

  D) Virtual Memory

  E) CU

  F) ALU

  G) L1 Cache

  H) L2 Cache

  I) MAR

  J) MDR

  K) CIR

  L) PC

  M) ACC

  
• Cache memory

  A piece of temporary memory. It can refer to a part of the RAM, storage disk, CPU, or an area for storing web pages.
• RAM (Random access memory)

  Volatile memory that is constantly being written to and read from. It does not retain its contents without a constant supply of power. When a computer is turned off, everything stored in its RAM is lost.
• CPU/processor (Central processing unit)

  The brain of the computer that processes program instructions.
• Data


  Units of information. In computing there can be different data types, including integers, characters and Boolean. Data is often acted on by instructions.
• Instruction

  A single action that can be performed by a computer processor.
• Cache memory

  • Data and instructions can be transferred to and from cache memory more quickly than from RAM
  • Cache memory is used to temporarily hold data and instructions that the processor is likely to reuse
  • The more cache memory a computer has, the faster it runs
  • Cache memory is more expensive to build than RAM, so it tends to be very small in size
• Types of cache memory

  • L1 cache
  • L2 cache
• L1 cache

  Extremely fast transfer rates, but very small in size. The processor uses L1 cache to hold the most frequently used instructions and data.
• L2 cache


  Bigger in capacity than L1 cache, but slower in speed. It is used to hold data and instructions that are needed less frequently.
• Von Neumann architecture provides the basis for the majority of the computers we use today.
• The fetch-decode-execute cycle describes how a processor functions.
• Von Neumann architecture

  The processing architecture that all CPUs use, invented by John von Neumann. It stores a program in memory as instructions and executes them sequentially using the ALU, control unit and registers.
• Fetch-decode-execute cycle

  Describes how a processor functions
• General purpose computers

  • Computers designed to be able to carry out a wide range of instructions
• Data


  Units of information, including integers, characters and Boolean
• Instruction

  A single action that can be performed by a computer processor
• Binary


  A number system that contains two symbols, 0 and 1. Also known as base 2.