Topic 2

• Factors affecting CPU performance:

  • Clock speed
  • Cache size
  • Number of cores
• Clock speed:

  • Number of fetch-execute cycles per second
• Number of cores:

  • Number of processing units on each CPU
• Cache:

  • Memory faster than RAM and slower than registers, usually located on the CPU
• Embedded systems:

  • Single microprocessor with RAM, ROM, and CPU
  • Used to control a device using simple inputs
• Embedded systems are essential for specific functions in digital devices

  • For example, a dishwasher's heating function or a satnav's communication with satellites
• Examples of embedded systems in cars:

  • Cruise control
  • Engine cooling fan
  • Interior fans and temperature control
  • Interior lighting
  • Rear cameras and remote parking
  • Infotainment systems
  • Engine control unit (ECU)
• Embedded system:

  
  

  CPU speed- Typically slow

  Software- Has one purpose and cannot install new software

  Storage- Programs stored on ROM

  Reliability- Typically very reliable

  
  

  General purpose machine:

  
  

  CPU speed- Typically very fast

  Software- New software can be installed

  Storage- Programs stored on hard drives

  Reliability- As it runs on many software programs, it may be less reliable and need restarting the device
• Levels of cache memory:

  • Level 1 cache: extremely fast but small (2-256KB), located on the CPU
  • Level 2 cache: fast, given to each core (256KB-8MB)
  • Level 3 cache: slower than L2 but faster than RAM, shared between all cores (4MB-50MB)
• Benefits of cache:

  • Level 1 cache holds data used most often for quick access
  • Level 2 cache is accessed about 90% of the time, reducing CPU wait time for data from main memory
• Effect on speed of cache:

  • Cache is faster to access than RAM
  • Instructions and data fetched are stored in cache for quick retrieval
  • Having all loop instructions in cache speeds up execution
• Processor Speed:

  • 1 cycle per second = 1Hz = 1 instruction per second
  • 1kHz = 1000 cycles per second
  • 1MHz = 1,000,000 cycles per second
  • 1GHz = 1,000,000,000 cycles per second
• Multi-core processors:

  • Dual-core processor: 2 processors in one circuit, can perform 2 instructions simultaneously
  • Quad-core processor: 4 linked processors
  • Quad-core can be up to 4 times faster than single-core under ideal conditions
• Which is theoretically faster?

  1. Dual-core 2.7GHz with 4MB cache

  2. Quad-core 1.5GHz with 8MB cache

  3. Single-core 3.2GHz with 2MB cache

  4. Dual-core 3.2GHz with 4MB cache

  Rank in order of performance based on maximum cycles per second