Computer Systems

• The purpose of a computer is to take data, process it, then output it
• A computer system consists of hardware and software that work together to process data/complete tasks
• Embedded systems are computers built into other devices, like dishwashers, microwaves and TVs
• Embedded systems are often used as control systems - they monitor and control machinery in order to achieve a desired result
• Embedded systems are usually:

  • easier to design
  • cheaper to produce
  • more efficient at doing their task
• power supply = supplies power to motherboard, optical and hard drives, and other hardware
• case cooling fan = extracts hot air from the computer case
• CPU = the most important component, does all of the processing
• optical drive = for read/writing of optical disks
• Motherboard = the main circuit board in the computer, where hardware is connected
• The CPU:

  • the brain of the computer system
  • it processes all of the data and instructions that make the system work
  • the processing power depends on different characteristics like its clock speed, number of cores and cache size and type
  • The CPU architecture describes the main components of the CPU
• The CPU has 5 main parts:

  • Control unit - overall control of the CPU, main job is to manage the fetching, decoding and execution of program instructions
  • Arithmetic logic unit - does all of the calculations, uses registers to store immediate results of calculations
  • Cache - very fast memory, faster than RAM, stores regularly used data so that the CPU can access it quickly, low capacity, expensive
  • Clock - sends out a signal that continually cycles, synchronises instructions
  • Buses - collections of wires that are used to transmit data
• Fetch-Execute Cycle:

  1. Fetch Instruction - control unit reads the memory address, the instruction stored in that address is copied from memory to one of the registers
  2. Decode Instruction - the instruction that was copied from the memory is decoded by the control unit, control unit prepares for the next step
  3. Execute Instruction - the instruction is performed
• There are four different types of memory:

  • registers
  • cache
  • random access memory
  • read only memory
• Random access memory (RAM):

  • high speed, volatile memory
  • used as the main memory in a computer
  • all data, files and programs are stored while they're being used
  • slower than the CPU cache memory, but much faster than secondary storage
• volatile memory = temporary memory, requires power to retain its data
• non-volatile memory = permanent memory, keeps its contents even when it has no power
• Read Only Memory (ROM):

  • used as a main memory, but is non-volatile
  • ROM comes on a small, factory-made chip built into the motherboard
  • contains all of the instructions a computer needs to properly boot up
• Non-embedded systems:

  • usually have much more RAM than ROM because they often need to write data to main memory
  • ROM and RAM are usually stored on the motherboard
• Embedded systems:

  • usually have more ROM than RAM because they don't write much data to memory
  • don't tend to have secondary storage so ROM is used to store all programs
• CPU performance:

  1. Clock speed - the higher the clock speed, the more instructions that can be carried out per second
  2. CPU cores - the more cores a CPU has, the more instructions it can carry out at once
  3. Cache - the larger the CPU cache gives the CPU faster access to more data it needs to process
• Cloud storage is a service where files can be uploaded via the internet to a remote server
• Positives of the cloud:

  • users can access files from any connected device
  • files can be shared with others or made public
  • easy to increase how much storage is available
  • no need to buy expensive hardware to store data
  • cloud host provides security and backups for you
  • can be cheap if not much storage is required
• Negatives of cloud:

  • need connection to the internet to access files
  • upload/download speed depends on bandwidth
  • dependent on the host for security and backups
  • stored data can be vulnerable to hackers
• How is data in Optical Storage devices read?

  • the shiny surface of the CD contains lands and pits
  • shine a laser beam on the surface and detect changes in position of the beam
  • if the beam reflects, it is a land and is stored as a binary digit 1, if the beam is not reflected, it is a pit and it stored as a binary digit 0
• Solid state drives:

  • fast and reliable secondary storage
  • no moving parts
  • tend to use flash storage - stores data in electrical circuits by trapping at electrons
• Advantages of Hard Disk Drives:

  • cheaper
  • higher capacity
  • longer read/write life
• Advantages of Solid State Drives:

  • faster
  • silent
  • shock-proof