computer systems - system architecture

• PC Case

  The enclosure that contains most of the components of a computer.
• PSU

  Power Supply Unit; The box inside the computer case that receives power and converts it to provide power to the motherboard and other devices.
• Motherboard

  The main board in the computer, also called the system board.
• CPU

  Central Processing Unit; executes instructions of a computer program
• RAM

  Random Access Memory, the computer's short-term memory for data currently in use
• HDD

  Hard Disk Drive; Computer's non-volatile long-term storage
• I/O devices

  allows users to input data into the computer or receive a data output from the computer itself (keyboard, monitor, speakers, mouse)
• primary storage


  the computer's main memory where the computer can store data and instructions that are currently in use (two main types are RAM and ROM)
• secondary storage

  the memory in which the computer can store data and instructions that are not currently in use ( hard disk drive, solid state drive, compact disc, flash)
• general purpose systems

  systems that are capable of performing many different tasks (PCs, Macs, Smartphones)
• embedded device


  a computer system which is built into another device to support its operation (washing machines, digital cameras, sat-navs)
• von neuman architecture

  The standard design model for computers
• arithmetic logic unit (ALU)


  performs all arithmetic operations (addition and subtraction) and all logic operations (sorting and comparison or boolean solutions)
• control unit (CU)

  coordinates the fetch-decode-execute cycle, decodes instructions, sends control signals to hardware (two main components are the clock and decoder)
• program counter (PC)

  Holds the memory location address of the next instruction to be performed by the CPU
• memory data register (MDR)


  holds the data or instructions fetched from memory or waiting to be stored to memory
• memory address register (MAR)


  holds the address of the location where data can be retrieved or stored
• accumulator (ACC)


  holds the result of the calculations and operations performed by the arithmetic and logics unit (ALU)
• fetch (in FDE)

  • the PC holds the address of the next instruction
  • the address is copied into the MAR
  • the instruction is fetched from memory and sent to the MDR
  • it is then copied to the CIR
  • the PC is incremented (OR... The instruction is fetched from the memory to the CPU)
• decode (in FDE)

  the control unit decodes the instruction in the CIR
• execute (in FDE)

  • the CPU executes the instruction
  • results may be stored in the accumulator (ACC)
• factors that affect CPU performance

  clock speed, cache size, number of cores
• clock speed

  The speed of a computer's CPU is measured in hertz. This indicates the number of fetch-decode-execute cycles that can run per second. (contains BIOS)
• cores

  A processing unit within a CPU. CPUs can have multiple cores.
• cache memory


  A type of memory used to temporarily store frequently used data for quick access; similar to RAM but faster.
• whats the difference between storing data and addresses

  addresses are stored in the Memory Address Register and data is stored in the Memory Data Register
• how does cache affect CPU performance?

  more cache reduces the need to fetch instructions from RAM (which is slower), therefore more cache improves CPU performance.
• how does clock speed affect CPU performance?

  the higher the clock speed, the greater the number of instructions that can be carried out per second
• how do cores affect CPU performance?

  the more cores a CPU has, the greater the number of instructions it can process in a given space of time.
• advantages of embedded systems

  their limited number of functions means they are cheaper to design and build, they tend to require less power, they do not need much processing power.
• advantages of von neumanns architecture

  contents of RAM can be used in the system as both data and instructions
• disadvantages of von neumanns architecture

  the processor may have to wait longer for the data/instructions to arrive (bottleneck)
• overclocking


  the CPU clock is set to run faster than the CPU is normally set to, this makes the CPU run hotter and so extra cooling fans also have to be purchased
• bus

  a set of wires which transfer data or power between components inside the computer
• volatile memory


  storage (such as RAM) that is wiped clean when power is cut off from a device.
• non-volatile memory

  Memory that retains contents when power is turned off, such as ROM
• cloud storage


  form of computer data storage where data is stored remotely in off-site locations
• advantages of cloud storage


  access your data anywhere, low cost
• disadvantages of cloud storage


  requires internet, data breaches, cost to buy more
• how does the HDD work


  1. disk spins 2. read/write head moves above disk and reads data 3. data is displayed as N/S 4. converted into 1(N) and 0(S) 5. these are on circles called tracks and parts of it called sectors