Hardware

Hardware

1. CPU

   • Responsible for all the processing of data a computer does
   • Where?
     • In the microprocessor
     • On the motherboard
     • Underneath a big piece of metal - heat sink.
       • The heat sink is needed to draw out the heat the CPU produces so it does not damage the processor. The CPU fan then vlows the hot air out the computer
   • Inside the CPU are millions of transistors
     • Transistors are electrical switches that built a circuitry and local gates inside the CPU - helpto control current through circuit board
   • Main parts
     • Control Unit
       • Coordinates parts of the processor when an instruction is received
     • Arithmetic Logic Unit (ALU)
       • performs calculations and comparisons
   • Works in 3 steps: Fetch-Execute cycle
     • 1. Fetch
       • All instructions and data for CPU are stored in the memory as binary. Through the DATA bus, the instruction is received from memory to CPU
     • 2. Decode
       • Instruction has been loaded into the CPU, and this step is working out what the instruction means. Done by Control Unit
     • 3. Execute
       • Comptuer carries out instruction, which could be a number of things such as loading data from meory or performing a calculation. Done by ALU
         • After CPU has read contents of PC, it updates it so it points to the next instruction
     • A register is a storage location for data in the CPU
       • The Program Counter (PC) is a type of register that holds the address of the next instruction waiting to be executed.
         • The instruction is transmitted to the memory through the ADDRESS bus and returned to CPU through DATA bus.
   • Clock speed
     • Frequency of fetch-execute cycle depends on clock speed of CPU
     • Measured in Herz (1Hz - can do one thing per sec)
       • Bigger measurements such as mega/gigahertz used as clock speed is much faster
     • Higher clock speed = faster computer

2. Cache

   • Small area of memory that is quick for the CPU to access
   • Comptuer stores regularly used items in the cache so the loading time is less
     • This is why web pages open quicker the second time they are visited, because the first time they are saved in the cache and the next time it opens it from the cashe and updates the bits that have changed
       • This makes it faster as it is not loading over an internet connection
   • Can be used to speed up the time it takes to load instructions into the CPU
     • When instructions are ready to be executed they are loaded into cache. Faster to read so is executed quicker
       • When CPU fetches instruction from memory, it checks the cache first
   • Cannot be used instead of RAM entirely as it is very expensive. Much more can be stored on the RAM than the cache for the same price
   • Faster than RAM as it is located between RAM and CPU

3. Processors and cores

   • Can speed up computer by having more processors working at same time
   • When there is more than one processor on the same chip, they are called cores.
     • A processor with two cores is a dual core processor
     • A processor with fore cores is a quad core.
       • There are also some processors with three cores - they are often quad cores with one disabled.
   • If there is multiple software, different programs can be handled by different cores
     • However, parallel processing is when several cores work on the same program
       • The more cores there are the quicker the program can run
         • However, extra cores do not help if an algorithm requires the outcome of previous steps before it can more onto the next step
   • Basically, by having a multi-core processor can improve performance when running several programs at the same time but having two cores will never be as fast as having one core running at twice the speed

4. Binary technology

   • Analogue technology uses continuous streams of data, e.g. sound files could get shown as continuous curved wave
   • Digital (binary) technology uses strings of values which represent data, e.g. wave would have measurements take from various points in its amplitude
     • Binary is a system of encoding data using only 1s and 0s - the base 2 system. Each 1 or 0 is a bit
     • These numbers will then get converted into binary
   • The small circuits in computers are composed of individual electronic components, such as transistors and capacitors which are all connected with conducted components and wires
     • This allows different operations to be performed, such as moving data from one location to another
     • Binary is measured by the output of a circuit. If the voltage is greater than the threshold then it is measured as 1 and vice versa
   • Computers use binary values rather than analogue because it is much faste to determine whether a device is on or off than measure an analogue value of property
     • Because of binary computers can work very quickly and perform quick operations frequently

5. Logic gates

   • Mainly small transistors and capacitors that are used to store data, wired together to make a circuit which performs simple, logical calculations
   • Each logic gate has at least one input, and an output in the form of binary digits
   • AND gate
     • Combines Boolean values of two inputs. If they are both true, the output will be true. If both are false, the output is false
   • OR gate
     • Combines Boolean values of two inputs. If either one is true, the output is true. If both are false, output is 0.
   • NOT gate
     • Will always give output that is the opposite of the input
   • A truth table is a method of recording all possible input combinations of logic gates and determing the output. Useful for testing whether a logic gate is producing the correct results

6. RAM

   • Random Access Memory
     • 'random' meaning that any byte of data can be accessed fast, in any order and at any time regardless of the time of creation
   • Can take data and put it anywhere, and can be edited without having to go through the whole lot of data
   • It can be read and written to
   • It is volatile, meaning it loses all of its contents if the electricity supply is switched off
   • Temporary storage location
     • Can also sometimes be used as permanent storage location as computer can read from and write to quicker
   • Loads programmes
   • Acts as memory address
     • Because RAM provides a unique address for data stored in it, it is possible for the CPU to read, modify and write to memory
   • Allows you to write values and store large amounts of data temporarily whilst executing programs
     • When a program is closed the computer deletes the information from the RAM, providing space for the next use
   • When a software application is loaded, the program gets copied from the hard disk to the RAM - it then travels to the CPU at high speed
   • It is made from microchip
     • So it contains no moving parts and stores data electronically, so had faster access time than secondary storage, but is slower than cache
   • Can store many values in an address.
   • Types of RAM
     • DRAM (Dynamic RAM)
       • Each cell stores bits with capacitors and transistors. DRAM chips have to be recharged frequently or they lose their circuit
     • SRAM (Static RAM)
       • Each cell stores bits with a six-transistor ciucuit. Does not need recharging as often as DRAM and can hold contents for longer. Is able to retain values indefinitely as long as power is on
   • RAM's capacity
     • Varies. Personal computers have SIMMS or DIMMs (Single/Double Inline Mmeory Modules)
       • Can be removed and replaced, whereas mobile phones and tablets have built-in memory
       • Early SIMMs were only about 128 kb, but are thousands of times bigger now due to Moore's Law
         • Moore's Law - computer power doubles every two years
     • The more RAM a computer has, the less virtual memory it requires for page swapping to disk, so program instructions can be held in memory - faster.
     • It is possible to replace the size of RAM by adding more chips
     • The processor's performance depends on how quickly it can access memory. If this is slow, the RAM becomes the bottleneck (part that is slowing the computer down)
       • This slows the fetch-execute cycle. The faster the memory access, the higher the processor's performance
     • If the processor accesses memory not currently in the RAM, it swaps out the page of the RAM and pulls in the required data
       • This is possible as secondary storage is very large but the access speed is very slow

7. ROM

   • Read-only memory
     • Cannot write memory to that location
   • Non-volatile - does not need power to keep its contains and stays put even without electricity supply
   • BIOS - Basic Input Output System
     • Stored on a ROM chip on the PC motherboard
     • Contains the data and programmes that tell the computer how to start up and how to talk to other parts of the system
     • Tests and initiates the system and then loads the operating system and other programmes from a storage device, such as the hard disk
     • Raspberry Pi does not have BIOS; instead has a little area of ROM on the system on the chip, and when it starts up it tells the SD card to load in the operating system
   • Smart phones have a an area of ROM that tells the phone how to start up, talk to the screen etc.
   • Very important, as without it a device would not even start up
     • Permanentely stores the programmes and data needed to boot that system, e.g. the BIOS in the PC
   • Can only store pre-programmed sets of instructions such as boot sequence

8. Virtual memory

   • When some of the storage area on the hard drive is used to act as 'pretend' or 'virtual' memory
   • Acts as an extension to physical memory, i.e. RAM
   • Used when physical memory is filling up pages that are not currently needed. It can be moved into virtual memory, freeing up space
     • When it is needed again it can be moved back from virtual memory to physical memory
     • 'pages' are small fixed divided chunks of memory. We can store some pages in virtual memory
   • 'Disk thrashing' - when a computer spends too much time swapping pages back and forth between physical and virtual memory, slowig down the computer
   • Using virtual memory is always slower than physical memory alone. The more RAM you have, the less virtual memory you need.

9. Efficiency

   • As the CPU works at an extremely fast speed that cannot be matched by the RAM, the RAM becomes a bottleneck
     • Static RAM (SRAM) is the solution to this problem. It is much faster than the main RAM but also more expensive. It can be used as cache memory
       • The price is not an issue as only a small amount is used, to store recently and frequently used data, where the CPU chekcs first
   • The larger the cache memory, the slower it becomes, so there are separate levels
     • Level 1
       • Fastest, smallest and closest to CPU. Contains the most frequently acessed data and is checked first by CPU
     • Level 2
       • Slower than level 1 cache, but still quicker than main memory. Bigger and further away from CPU. Contains the most frequently accessed data
     • Some processors may have 3 or more levels of cache

10. Storage devices

    • Magnetic
      • such as most hard drives
      • Consists of stacks of non-removable platters with heads to read the data as the platters spin around
    • Optical
      • such as CDs, DVDs, Blu-rays
      • Uses light from laser to detect reflections from surface of data area. Surface has dyed layer that changes after laser is shined.
        • The colour difference is detected when it is read
    • Flash memory
      • Special type of RAM called EEPROM (Easily Erasable Programmable Read Only Memory
      • Has various advantages over other types of storage media
        • Speed (quicker to read and write to than other types of storage media)
        • Requires less power
          • Uses battery
            • Is mobile
          • Has no moving parts so is solid state memory
      • Tends to be used in smaller amounts as it costs more per MB
      • Flash memory cards usually used in small devices such as mobile phones and digital cameras
    • Solid state memory
      • Much faster than magnetic storage devices.
      • Contains no moving parts so more durable than magnetic
      • Constant writing and rewriting of data can cause deterioration and eventual failure
        • Limits their use in critical systems
      • e.g. USBs and RAM chips
    • As technology devlops storage devices are requiring more capacity, faster access time and being physically smaller
    • Over time have got larger and cheaper, and are a large variety of them
    • When choosing a storage device, different things should be considered
      • capacity
        • How much data it will store, and which one fits your needs more. CD stores 700 MB, blue-ray 128 GB
      • portability
        • How easy it is to carry around, e.g. USB more portable than CD
      • reliability
        • i.e. how many times it can be read and written to before it becomes useless - likelihood of failure
      • durability
        • whether it is resistant to things like pressure, temp, accidental damage, CD is not
      • speed
        • how fast data will be read from and written to the device
    • storage capacity
      • CD stores 700 MB data and DVD stores 4.7 GB
      • Flash memory cards 512MB to 64GB
      • Hard disks 512MB to 1TB

11. Input and output devices

    • Input devices
      • Mice
        • for tracking a user's movement
      • Keyboards
        • for typing in characters
      • microphones
        • for recording audio
    • Output devices
      • monitors
        • displays data stored on system
      • speakers
        • to listen to audio stored on computer
    • Can be combined, e.g. a touch screen
    • 'Assistive technologies'
      • To enable users with specific needs to interact better with technology
        • Concept keyboards with larger keys
        • 'Tracker balls' instead of mouse. Used by moving ball and using buttons
        • Blow and sip tubes connected to computer
        • Speech recognition (input)
        • screen reader (output)
        • braille printer (output)