lecture3

• Performance


  An important attribute when choosing among different computers
• Running a program on two different desktop computers


  The faster one is the desktop computer that gets the job done first
• Running a datacenter with several servers running jobs submitted by many users

  The faster computer is the one that completed the most jobs during a day
• Response time

  The time between the start and completion of a task, also called execution time
• Total time required for the computer to complete a task

  • Disk accesses
  • Memory accesses
  • I/O activities
  • Operating system overhead
  • CPU execution time
• Processor speed


  The speed of the processor, measured in GHz (gigahertz), determines how quickly the computer can execute instructions and process data
• Memory


  The amount and speed of the memory, including RAM (random access memory) and cache memory, can impact how quickly data can be accessed and processed by the computer
• Storage


  The speed and capacity of the storage devices, including hard drives and solid-state drives (SSDs), can impact the speed at which data can be stored and retrieved
• I/O devices


  The speed and efficiency of input/output devices, such as keyboards, mice, and displays, can impact the overall performance of the system
• Software optimization


  The efficiency of the software running on the system, including operating systems and applications, can impact how quickly tasks can be completed
• Throughput


  The total amount of work done in a given time
• CPU execution time


  The total time a CPU spends computing on a given task, excluding time for I/O or running other programs
• Performance


  Inversely proportional to execution time
• Clock speed


  The rate of pulses, or clock cycles, that govern the operations performed by a processor
• A 1-GHz processor receives 1 billion pulses per second
• Clock cycle


  One increment, or pulse, of the clock
• Cycle time


  The time between pulses
• Basic Operation of Computer

  To execute a program/ command/ set of instructions
• Basic Operation of Computer


  1. Instructions are stored in computer memory

  2. Data is loaded into computer memory through input devices

  3. Data is processed

  4. Result is stored in memory or sent to output port

  
• Processor


  • Contains arithmetic logic unit, control unit, and registers for temporary storage and special functions
• Instruction Execution


  1. Fetch instruction

  2. Read contents of memory location A

  3. Read contents of memory location B

  4. Add the two values

  5. Write result to memory location A

  
• Program Counter (PC)


  Contains the memory address of next instruction to be fetched

  
• Instruction Register (IR)


  Holds the instruction which is currently being executed

  
• Memory Data Register (MDR)


  Facilitates communication with memory, contains data to be written or read

  
• Memory Address Register (MAR)


  Holds the address of the location that is to be accessed

  
• Processor Registers


  • Program Counter
  • Instruction Register
  • MDR
  • MAR
  • General purpose registers (R0 to Rn-1)

  
• Program Counter (PC)


  • Monitors the execution of instructions, keeps track of which instruction is being executed and what the next instruction will be

  
• Instruction Register (IR)


  • Contents are available to the control unit, which generates the timing signals that control the various processing elements involved in executing the instruction

  
• Instruction Execution Process


  1. PC is set to point to first instruction

  2. Contents of PC are transferred to MAR

  3. Read control signal is sent to memory

  4. Addressed word is fetched from memory and loaded into MDR

  
• Bus Structures and Operation