3.1 von neuman and computer architecture

• stage 1 of FDE

  control unitreadsinstruction from memory

  addressof location of instruction isstoredinprogram Counter (register)

  (during this signals generated alongcontrol busto tell other components in computer what to do)

  CU ensures synchronisation of data flow and program instructions
• registers


  small amounts of high-speed energy

  
  

  store data needed during processing
• CIR


  current instruction register

  
  

  - stores current instruction being decoded and executed
• ACC


  accumulator

  
  

  used when carrying out ALU calculations, it stores data temporarily during the calculations
• MAR


  Memory Address Register

  
  

  stores the address of the memory location currently being read from or written to
• MDR


  memory data/buffer register

  
  

  - stores data which has just been read from memory or data which is about to be written to memory
• PC


  program counter

  
  

  stores address where the next instruction to be read can be found
• address bus


  carries memory addresses from the processor to other components e.g primary memory + input/ output devices
• control bus


  carries control signals from processor to other components

  also carries the clock's pulses
• Data bus


  carries the actual data between the processor and other components
• components in the CPU

  CARBS

  
  

  control unit

  arithmetic logic unit

  registers

  buses

  system clock
• How MAR and MDR work together

  - The MAR knows where to look for data in RAM,

  
  

  - the MDR keeps hold of that data until it's ready to be used by the CPU

  
  

  content in RAM wirtten onto MDR in CPU

  this address now written into MAR

  write signal send to computer memory and the content written into correct memory
• Central Processing Unit (CPU) contains?


  - control unit ( CU )

  - arithmetic logic unit (ALU)

  - registers and buses

  
  

  Also

  -system clock

  Primary memory
• A microprocessor is a


  - is an integrated circuit (microchip) designed to process instructions

  - It is the most important, and usually the most expensive, component of a digital device
• Von Neumann Architecture introduced?

  - concept of CPU

  - processor able to access memory directly

  - computer memories could store programs as well as data

  - stored programs made up of instructions which could be executes in sequential order
• Components of the CPU :

  
  

  ALU


  - Performs arithmetic and logical operations on data (e.g ADD, MULTIPLY)...

  - Boolean logic operations such as AND, OR...

  - allows multiplication + division using shifting operators

  
  

  - computers can have more than one ALU
• Components of the CPU :

  
  

  Control Unit

  - reads instructions from memory

  
  

  - signals are generated during Fetch-Decode-Execute cycle to control all components of the computer

  
  

  - computer unit synchronises data flow and program instructions throughout the computer
• Components of the CPU :

  
  

  Registers

  - registers can be general purpose or special purpose

  
  

  - high speed areas of memory within a CPU - used to store small amounts of data, address of next instruction to be executed or current instruction being decoded.

  
  

  - registers include : current instruction registers (CIR), accumulator (ACC), memory address register (MAR), memory data/buffer register (MDR), program counter (PC)

  
  

  - are used in FDE cycle
• System clock


  - used to produce timing signals on the control bus to ensure all functions are synchronised

  
  

  - changing clock speed can improve performance but there is always the risk of overclocking —> can lead to system crashes
• Components of the CPU :

  
  

  System buses

  3 types of buses

  - transfer data and control throughout computer

  
  

  - use parallel data transfer and width of bus can ber according to bus architecture

  
  

  Address bus - unidirectional - carries addresses throughout the system

  Data bus - bidirectional - allows data to be carried to/from CPU/memory and to/from input-output

  Control bus - bidirectional - carries signals from the CU to all computer components

  
  

  Width of bus determines the word length/size and the performance of the computer
• Components of the CPU :

  
  

  Memory

  RAM

  Memory


  -Random access M (RAM) holds data, programs and part of the operating system currently in use

  
  

  - often known as Immediate Access store (IAS)

  
  

  - all data being used in programs needs to be transferred to the RAM

  
  

  - Memory is made up of an address and its content; address identifies the location of data and instructions

  
  

  - all memory location are unique

  
  

  - primary memory also includes read-only memory (ROM) which cannot be altered, contains the start- up routines for the computer
• Fetch part of FDE cycle (4)

  1) PC contains address of memory location of next instruction to be fetched from me memory (MAR)

  
  

  2) address is copied from PC to the MAR using the address bus

  
  

  3) contents of memory location contained in MAR copied into MDR

  
  

  4) contentes of MDR then copied to CIR and the PC is incremented by one so next instruction can be processed
• Decode part of FDE cycle

  1) instruction now decoded so that it can be interpreted by next part of cycle
• Execute part of FDE cycle

  1) CPU passes decoded instructions as a set of control signals to appropriate computer components

  
  

  2) this allows each instruction to be carried out in a logical sequence
• Cache?


  Store frequently used instruction and data, can speed up CPU performanance

  - larger cache better CPU performance
• Cores


  Once core made up of an ALU, A CU and registers.

  
  

  A quad core has four independently operating units that can read and execute CPU instruction
• Overclocking


  Caused by changing clock speed in Basic Input/ Output System

  - can lead to over heating and non-synchronised instruction s

  - which can cause computer to crash
• Embedded system?


  A computer system with a dedicated function within a larger electrical or mechanical system.
• Parts of embedded system

  Microcontroller : made up of a CPU with RAM, ROM and peripherals all embedded on a single chip to carry out a specific task

  
  

  Microprocessor : Integrated circuit consisting of CPU ONLY

  
  

  System on a chip : may contain a microcontroller as one of components : usually includes CPU, memory, input/output lifts and secondary storage

  All on a single chip
• General makeup of an embedded system

  Analogue or digital input, embedded systems can contain sensor input, mechanical components, actuators and software, modern systems use dual and quad core CPUs and variety of I/O connections
• eg embedded systems


  - washing machines

  - vending machines
• Benefits of embedded systems

  1.to perform a small number of specific tasks.

  
  

  2.Cheap to produce

  
  

  3.Use very little power(energy efficient)

  
  

  4.Reliable because:

  perform specific tasks

  software cannot easily be updated once manufactured.

  components are small to other computer systems
• Drawbacks of embedded systems

  1) can be difficult to upgrade some devices to take advantage of new technology

  
  

  2)troubleshooting faults in the device is a specialist task

  
  

  3) any device that can be accessed over the internet is also open to hackers viruses and so on