3.1 Computer Architecture

What is the role of a CPU in a computer?

  • The CPU processes instructions and data that are input into the computer so that the result can be output

What is a microprocessor?

  • a type of integrated circuit on a single chip

What is the purpose of a register?

  • Register is a high speed storage area
  • Used to hold memory location or an instruction
  • ..temporarily
  • Used within the fetch execute cycle

What is the ALU?

  • Carries out calculations
  • Carries out logical operations
  • Holds temporary values during calculations
  • …in a register called the accumulator

What is the function of the control unit?

  • Controls operation of memory, processor and input / output
  • Instructions are interpreted
  • Sends signals to other components telling them “what to do”

Fetch Decode Execute

Registers used in the Fetch Execute Cycle

  • Program Counter- holds the address of the next instruction to be executed
  • MAR- Holds the address to fetch the data (from the Program counter)
  • MDR- Holds the data which has just been read from memory
  • CIR- holds the instruction that is to be decoded and executed
  • ACC- holds the results temporarily at the end of the fetch execute cycle

Describe the stored program concept when applied to the Von Neumann model (4points)

  • The program is stored on a secondary storage device
  • Data and instructions are moved to memory / RAM
  • Data and instructions are stored in the same memory / RAM
  • Data and instructions are moved to registers to be executed
  • Instructions are fetched one at a time

Explain how an instruction is fetched in a von Neumann model computer

  • PC holds the address of the instruction
  • The address held in PC is sent to MAR..
  • ..using the address bus
  • MAR goes to location in memory where the instruction is stored
  • Instruction sent to MDR..
  • ..using data bus
  • Instruction sent to CIR
  • Control unit sends signals to manage the process..
  • ..using the control bus

BUSES IN FETCH EXECUTE CYCLE:

Address Bus

  • it is UNIDIRECTIONAL
  • Carries / transports an address / location ..
  • .. of the next item to be fetched
  • Data travels one way (unidirectional)

Data (bus)

  • it is BIDIRECTIONAL
  • Carries / transports data / example of data ...
  • .. that is currently being processed // that will be / has been processed
  • Data can travel in both directions (bidirectional)

Control (bus)

  • it is BIDIRECTIONAL
  • Carries / transports signals
  • Control / directs the actions of the CPU / processor
  • Can be either Unidirectional or Bidirectional

BUSES IN FETCH EXECUTE CYCLE:

Core

  • one core is made up of an ALU, a CU and the registers
  • used to perform the fetch-execute cycle
  • to process/execute an instruction

Cache

  • cache is fast access memory (close to the CPU)
  • cache stores frequently used instructions / data
  • ... more cache means more instructions / data can be transferred faster

Clock/System Clock

  • synchronise operations
  • ... by creating timing signals
  • to keep track of the date and time / timestamp files
  • to process operations in the correct order / sequence

Factors affecting performance of a CPU:

Multiple cores(eg dual core instead of single core):

  • It can process two instructions simultaneously
  • ..increasing the performance
  • to process an instruction
  • however it doesn't double the speed of execution as the CPU needs to communicate with each core

Increasing cache:

  • cache stores frequently used instructions / data
  • ... more cache means more instructions / data can be transferred faster
  • ... less swapping between RAM and cache

Overclocking/increasing clock speed

  • The faster the clock speed the more instructions can be run per second
  • ...however, there is a limit on clock speed because the heat generated by higher clock speeds cannot be removed fast enough

Address+Data bus width

  • Increasing the address bus width, increases the number of upcoming instruction addresses can be transferred from memory
  • Increasing the data bus width increases the number of instructions that can be carried for execution

What is a CPU instruction set?

  • A list of all commands that can be processed by a CPU and the commands are machine code

Embeded Systems

What is an embedded system?

  • a combination of hardware and software designed to carry out a specific set of instructions
  • It is built into a device
  • It has a single purpose
  • It runs on firmware
  • It does not have additional firmware

Pros & cons of embedded systems

  • Small in size (fit easily fit in big devices)
  • Relatively low cost
  • Consume very little power
  • May be difficult to upgrade
  • - Troubleshooting faults becomes a specialist task

You may need to know how embedded systems is used with a given example