Systems Architecture

• CPU components

  • Control Unit
  • Clock
• Factors affecting CPU performance

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

  Cycles per second, measured in hertz (Hz)
• Processor cores

  The number of duplicate processing units (cores) placed in one CPU
• Cache

  Memory on the CPU that is faster than RAM but slower than registers
• Clock speed

  1. Everything in a computer happens on the pulse of the internal clock

  2. The faster the clock speed, the faster the instructions are processed
• One cycle per second = 1 hertz (Hz) = 1 instruction carried out each second
• 1 kilohertz (kHz) = 1000 cycles per second
• 1 Megahertz (MHz) = 1,000,000 cycles per second
• 1 Gigahertz (GHz) = 1,000,000,000 cycles per second
• Multi-core processors


  • A dual-core processor has two processors in the same integrated circuit, linked together
  • A quad-core processor has four linked processors
• A quad-core processor working on many different tasks simultaneously

  Can be up to four times faster than a single-core processor
• If the computer is running a single program

  It is not necessarily any faster, since the program may have been designed to only run on one core
• Cache memory


  • A small amount of very fast, expensive memory in the CPU
  • It can be accessed faster than regular main memory (RAM)
• RAM is relatively slow memory to access and it is further away from the processor than cache

  It takes longer to retrieve an instruction or data from RAM than from cache
• Program instructions and data that are fetched


  Are stored in cache in case they are needed again soon
• Levels of cache memory

  • Level 1 cache: extremely fast but small, located on the CPU, each core has its own
  • Level 2 cache: very fast, but a little slower than level 1 cache, typical size 256KB-8MB
  • Level 3 cache: the slowest type of cache, but still faster than RAM, located on the CPU, stores 4MB-50MB, shared between all cores
• The benefits of cache

  • The data used most often by the CPU is held in Level 1 cache so is available extremely quickly
  • In most systems, Level 1 cache is used about 50% of the time, with Level 2 cache being accessed about 90% of the time
  • This greatly reduces the time that the CPU has to wait for data from main memory
  • The size of the Level 2 cache is a major factor in determining the performance of the CPU
• Embedded systems


  • An embedded computer is a single microprocessor that includes RAM, ROM and a CPU
  • An embedded computer is frequently used to control a device using simple inputs
• Without embedded systems, a digital device would not be able to perform specific functions
• Characteristics of embedded systems vs general purpose machines

  • CPU speed: Typically slow vs Typically very fast
  • Software: Has one purpose and cannot install new software vs New software can be installed
  • Storage: Programs stored on ROM vs Programs stored on hard drives
  • Reliability: Typically very reliable vs May be less reliable and need restarting the device
• Common factors affecting CPU performance

  • Clock speed
  • Cache size
  • Number of cores
• Embedded system


  A single microprocessor that includes RAM, ROM and a CPU, frequently used to control a device using simple inputs
• Embedded systems


  • Dishwasher
  • Satnav
  • Microwave