Computer science UNIT ONE (NOT COMPLETED)

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  • UNIT ONE
    • Computational thinking
      • Abstraction
        • Removing unnecessary detail
      • Decomposition
        • Breaking large problems into smaller key problems which are easier to solve
      • Computational thinking
        • Using computers to solve problems
      • Algorithmic thinking
        • Using clear logic and algorithms (list of instructions) to solve problems
    • CPU (Central Processing Unit)
      • Clock Speed
        • Controls the number of cycles that can be run per second
      • Cores
        • The more cores the faster the processing speed
      • Cache
        • The more caches the faster the processing speed
          • Two levels of cache
            • Level One is very small, fast and expensive memory but located on the CPU
            • Untitled
      • Embedded Systems
        • Dumb programs
        • Found in washing machines, Alarm clocks, Ovens , Dishwashers
        • Microprocessor
      • Componants
        • MAR (Memory address register)
          • Holds the instructions for the data being fetched
        • MDR (memory data register)
          • Holds the data being fetched
        • Acumulator
          • Where the results of the ALU are stored
        • ALU (Arithmetic logic unit)
          • Performs all arithmetic and logic calculations
        • Program counter
          • Every time an instruction or piece of data is collected the PC increases by one
        • Cache
          • RAM - stored on the processor making it closer to the CPU meaning that the memory is faster to access increasing the Processor speed
      • Fetch- decode - execute cycle
    • Memory
      • RAM (Random Access Memory)
        • Volatile
      • ROM (Read Only Memory)
        • Non-Volatile
        • Loads the BIOS
          • Basic Input Output System
          • Loads the instructions to run the hardware
      • Virtual
        • Extends the memory and prevents the computer from crashing
      • Flash
    • Storage
      • Types of storage:Magnetic: Mechanical parts move over the disks surface to read and write data magnetically Optical: Lasers read and write data using light Solid State: Data is recorded onto solid memory chips without any moving parts
        • Magnetic
          • Basic Features
            • Disk containsconcentric circlescalled tracks
            • Each track is dividedinto sectors
            • Disk heads mountedon mechanical armsread and write the data
          • Advantages and Disadvantages
            • Cheap, vast storage capability, fast write speed
            • Lots of mechanical parts, durability an issue, sealed unit dueto disk head and platter precision and not very portable
          • Uses
            • Personal computers, storage of vast quantities of data
          • Capacity
            • 500GB - 6TB or greater
        • Optical
          • Basic Features
            • Data is stored as pits andlands burnt into a spiraltrack circulating outwardsfrom the centre
            • From this signal, 0s and 1scan be derived fromreflections or no reflections
          • Capacity
            • CD-ROM – up to 720MbDVD – up to 8.4GbBlu-Ray – up to 50Gb
          • Advantages and Disadvantages
            • Cheap, very easily portable, takes up little space physically
            • Less storage capacity compared to other typesEasily damaged / scratched, requires a CD readerSlow write speeds
          • Uses
            • Songs, videos and other multi-media storage, backup andarchiving of data
        • Solid State Drives (SSD)
          • Basic Features
            • Solid-state disks usenon-volatile flash memory tostore information
            • Very fast burst read/writespeeds due to data beingphysically close and easy torecover
            • No mechanical or movingparts
          • How it works
            • Large electric current used to force electrons through a barrier and trap them on the other side. They remain on the other side until “flashed” with anew current, hence the name
              • Solid State Drives (SSD)
                • Basic Features
                  • Solid-state disks usenon-volatile flash memory tostore information
                  • Very fast burst read/writespeeds due to data beingphysically close and easy torecover
                  • No mechanical or movingparts
                • How it works
                  • Large electric current used to force electrons through a barrier and trap them on the other side. They remain on the other side until “flashed” with anew current, hence the name
                  • Advantages and disadvantages
                    • Highly durable, no moving parts, very fast read/write speeds,no noisy fan, faster start up times
                    • Expensive at present, less storage capacity / physical sizethan traditional hard disks
                  • Uses
                    • Portable computers,Military usage
            • Advantages and disadvantages
              • Highly durable, no moving parts, very fast read/write speeds,no noisy fan, faster start up times
              • Expensive at present, less storage capacity / physical sizethan traditional hard disks
            • Uses
              • Portable computers,Military usage
        • Flash memoery
          • Advantages: Low cost, portable, no moving parts, durable
          • Uses
            • Cameras, Mobile phones, USB memory sticks
      • Networks
        • Local Area Networks (LAN'S)
          • A LAN operates on a single site such as a school orsmall business using their own cabling systems
          • Advantages: Sharing resources such as printers saves money,You can access your files fromany computer in the network, Data is easy to back up as it isstored centrally on the server
          • Disadvantages:Purchasing the networkhardware is expensive, Managing a large network iscomplicated, Viruses may be able to infiltratethe network and infect everycomputer
        • Wide Area Networks (WAN)
          • A WAN uses cables, telephone lines, satellites andradio waves to connect, usually spread over a widegeographical area
        • Topologies
          • Star
            • Advantages: Fast data transfer as there arefewer data collisions, If one cable fails the otherworkstations are not affected
            • Disadvantages:Requires additional hardwaresuch as the central switch, If the central device fails thewhole network goes down
          • Mesh
            • Advantages No single point of failure – It is aself-healing network, Expansion and modification canbe done without disrupting thenetwork, Data can be transmitted fromdifferent devices simultaneously
            • Disadvantages:Can involve redundantconnections, Expensive to install cabling ifusing wired connections, Network maintenance andadministration is difficult
        • Network hardware
          • A Network Interface Card (NIC) in your computer or device
            • Untitled
          • Router: Sends data packets on their way in the best direction
          • Switch: Central, multi-plug adapter for computers and printers in a network :When a packet of data is received, it broadcasts the packet to all devices on the network
          • Switch: Smart multi-plug adapter only sends packets to the intended recipient, using its MAC address: Reduces network traffic and increases speed
        • Ethernet protocols
          • ‘Ethernet’ refers to a family of standard localnetworking ‘protocols’ or rules
          • It describes how devices should format data readyfor transmission between computers on the samenetwork

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    magiciskey

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    this is very helpful

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