Computing paper 1

Computing paper 1

1. Fetch - decode - execute cycle

   • Instruction fetched from memory
     • Instruction is decoded
       • Decoded instruction executed so CPU performs continuously
         • Process repeated
           • Instruction transferred to MDR
             • Adress of instruction to be fetched stored in MAR

2. Control unit

   • Controlls CPU
   • Executes instructions using fetch decode execute cycle
   • Controls flow of data in CPU to registers, ALU, and cache
     • ALU
       • Performs calculations and logic operations
       • Arithmetic logic unit
       • Has accumulator register which stores results of calculations
     • Cache
       • Very fast, small, expensive memory inside CPU
       • Faster than RAM but slower than registers
       • Stores frequently used data in CPU so easily accessible for use
       • CPU checks cache first then checks RAM if not in cache
       • L1 is quickesy with lowest capacity
         • L2 is slower but can hold more
           • L3 is slower but can hold more

3. Virtual memory

   • Used when RAM is running low
     • Used as if it is RAM
       • Much slower than RAM due to HDD read/write times
   • Secondary storage
   • Managed by operating system
   • Open files/data/programs saved to HDD
     • Moved back to RAM when needed by CPU

4. Factors affecting performance

   • Clock speed
   • Cache size
   • RAM
   • Number of cores
   • GPU
     • Graphics processing unit

5. Secondary storage

   • Characteristics of secondary storage devices
     • Size/capacity
     • Speed
     • Portability
     • Durability
     • Reliability
     • Cost