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J276/01 - Section 1 - Components of a Computer System (Secondary Storage…

- - - - As embedded systems are dedicated to a single task, they are usually easier to design, cheaper to produce, and more efficient at doing their task than a general purpose computer.
- - - - Read/write speeds are much slower compared to primary storage.
  - - - Specific examples are CDs, DVDs and Blu-Ray discs.
  - - - 1 byte per character + 10% for overheads.
      - For example, if you had a text file with 1000 characters, it will contain approximately 1000 x 1.1 = 1100 bytes.
        This then needs to be converted to KB so simply divide by 1000 which in this scenario gives you 107 KB.
    - - 256 colours = 8 bits per pixel (1 byte)
      - (Number of pixels x number of bytes per pixel) + 10% overheads (x1.1)
    - - 1) Find number of bytes in one record.
      - 2) Multiply by the number of records.
      - 3) Add 10% for overheads.
      - 4) Divide by 1000 to convert bytes to KB.
    - - bytesPerSample x SamplsPerSecond x channel x duration (s)
- - - - Over time the disk becomes more and more fragmented which makes reading and writing files slower as the read/write head has to move back and forth.
        
        Defragmentation software reorganises data on the hard drive to put fragmented files back together. It also moves files to collect all the free space together which helps to prevent further fragmentation.
    - - A full backup is where a copy is taken of every file on the system. They often use a lot of storage space. A full backup can take a longer time to create, but is faster to restore from.
        
        An incremental backup is where only the files created or edited since the last backup are copied. They use less torage space and are much quicker to create.
        But, a full system restore is slow - the last full backup must be restored, followed by every incremental backup since that point.
  - - - Graphical User Interfaces (GUIs) are easy for everyone by making them visual, interactive and intuitive.
      - GUIs systems are optimised for specific input methods. Android and iOS were created for touchscreen devices,
      - A User Interface allows the user to interact with a computer system.
      - A command-line interface is text based. Command-line interfaces are less resource-heavy than GUIs.
      - Command-line interfaces aren’t suitable for everyday
        users. They can be far more efficient and powerful than a GUI.
    - - Operating Systems that can run multiple applications at the same time are called multi-tasking OSs.
      - The OS helps the CPU carry out multi-tasking by efficiently managing memory and CPU processing time:
        
        A memory manager allocates certain applications certain
        memory addresses, to make sure their processes are placed into separate locations. So they don't overwrite each other.
        
        Only one application is processed by the CPU at a time so it must prioritise certain process in order to be efficient.
        
        OS moves the necessary parts of the application to memory, followed by additional parts when they are required. If they have not been used recently they are removed.
        
        OS organises the movement of data to-and-from virtual memory.
      - Operating Systems provide a platform to run applications.
    - - Drivers essentially act as a ‘translator’ for the signals between OS and hardware. Every piece of hardware needs one.
      - When a computer is booted up, the OS will choose the correct device drivers for the hardware it detects. If anything is new it installs the matching driver.
      - Operating systems use device driver software to communicate with internal hardware or peripherals connected to the computer system.
      - Updates may be installed automatically by the OS or manually by the user.
    - - Computers store data as files. Images, music, videos and spreadsheets are all just collections of data.
      - The OS is responsible for file management It also deals with the movement, editing and deletion of data.
      - The OS manages the hard disk. It splits the physical disk into storage sectors, decides which
        sectors to write data to, and keeps track of free space on the disk.
      - The OS also organises and maintains the hard disk with
        utility software like defragmentation software
    - - Provide a user interface, allowing a user to interact
        with the computer and vice-versa.
      - Provide a platform for different applications to run.
      - Communicate with internal and external hardware
        via the device drivers.
      - Allow the computer to multi-task by controlling
        memory resources and the CPU.
      - An Operating System (OS) is a complex piece of software found on most computer systems.
      - Deal with file management and disk management
    - - The OS is also responsible for user account control. User accounts allow different users to be granted access to specific data or resources on a computer system.
      - On most desktop operating systems each user has access to their own personal data and desktop, but cannot access other users’ personal data.
      - Operating Systems can be single-user or multi-user. Single users like windows 10 allow one user at once. Multi user allows several users to use the computer at the same time. Normally are on mainframes.
      - Operating systems may have anti-theft or password, or pin protected.
- - - - When RAM becomes full, virtual memory is used. Thrashing the disk is a term used when the processor is short of RAM.
        The process of using virtual memory includes RAM becoming full, the information that hasn't been used recently gets transferred to the secondary storage and every time that information is needed it has to be moved back to the RAM first. This process is known as paging.
        
        Using virtual memory can make a computer slow to respond when switching between applications or when using a memory-intensive application which is due to constantly moving between virtual memory and RAM just to keep the program running.
  - - - BIOS - stands for Basic Input/Output System. BIOS is a ROM chip that contains all the instructions a computer needs to boot up properly. The following four things sum up the main role of BIOS:
        Tests the hardware
        Locates the operating system (bootstrap loader)
        Loads the divers
        CMOS setup (allows you to set time, users etc.)
        
        Boot up/Boot strap - the first piece of code that runs when a machine starts and is responsible for loading the rest of the operating system.
        
        Firmware - permanent software stored on the ROM. It is used to control hardware or embedded systems. It makes the hardware work correctly in other words...
      - EEPROM is also known as flash memory. Flash memory is often used by ROM chips and is a very common type of non-volatile memory.
        
        It's used in SD cards, USB sticks and solid state drives. Flash memory is also a form of static RAM which means it doesn't lose charge whilst in use.