1.1 System architecture

• CPU ( Central Processing Unit)

  The function of CPU is to process data and instructions by doing Fetch-Execute cycle.
• Common CPU components :

  • ALU ( arithmetic logic unit )
  • CU ( control unit )
  • Cache
  • Register

  ~ MAR ( memory address register )

  ~ MDR ( memory data register)

  ~ Accumulator

  ~ PC ( program counter )
• ALU ( Arithmetic Logic Unit )

  • carries out arithmetic operations
  • e.g addition, subtraction, multiplication, division
  • performs logic operations on binary data
  • e.g AND, NOT, OR
• CU ( Control Unit )

  Coordinates all activities in the CPU:

  • manage fetch-execute cycle
  • control flow of data inside CPU (ALU, Cache…) and outside CPU (memory..)
• Cache

  • very fast memory
  • faster than RAM, slower than registers
  • stores regularly used data or instructions
• Registers

  • small amount of high speed memory
  • stores adresses or data currently being worked on
• MAR ( memory address register )

  stores address where data needs to be fetched from or stored
• MDR ( memory data register)

  Holds data or instruction that have been fetched from or to be stored in memory
• PC ( program counter )

  stores address of next instruction to be fetched ( gets ready for next instructio)
• Accumulator

  stores result of calculations done by ALU
• Von Neumann architecture

  
• Fetch- Decode- Execute cycle

  1. Fetch

  • Memory address from program counter is copied to MAR
  • instruction stored in MAR is copied to MDR
  • increment ( Increase) program counter to point to the address for next instruction

  2. Decode

  • instruction in MDR is decoded by CU
  • CU prepare for next step by loading values into MAR/ MDR

  3. Execute

  • instruction is executed ( data written to memory….)
  • cycle is repeated
• Factors affecting CPU:

  • Clock speed
  • Cache size
  • number of cores
• Clock speed

  • number of instruction a single processor can carry out per second = to 1 Hz
  • the faster clock speed, greater number of instructions carried out
  • BUT, if clockspeed too high, CPU can be overclocked and overheat resulting in crashes or permanent damage
• Cache

  • A larger cache gives CPU faster access to more data
• Number of cores

  • Each core in CPU can process instructions one at a time ( one core process one instruction)
  • the more cores a CPU has, the more instructions the CPU can process simultaneously (at the same time)
• Embedded system

  • A computer system built into a larger device with one main purpose

  characteristics:

  • more reliable
  • cheap to design and built
  • efficient at doing task
  • smaller in size, makes them compact size
• Embedded system

  • smoke detector
  • washing machine
  • microwave