IB Computer Science/Science Systems Life Cycle and Software Development/Systems Design

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System Design[edit | edit source]

Parts Of A System[edit | edit source]

The main parts of any computer system follow the input-process-output model of data flow:

Input Processes and Outputs.jpg

However, hardware also needs backing storage, as there is no permanent storage in the CPU:

Inputs Processes and Outputs for Hardware.jpg

Layers of software have also been implemented, so no direct contact with hardware is necessary:

Layers in computer systems.jpg

Data in a System[edit | edit source]

When data is in a system it is often shown in flow diagrams with the following symbols:


Data Capture and Output Presentation[edit | edit source]

  • Data Capture
    • Manual Data Entry - Keyboard, mouse (Example: adding client records to a database)
    • Direct Data Entry - OCR/OMR scanners, barcode scanner etc (Example: Lending a book or locating borrower details)
    • Automatic Data Entry - Sensors (Example: automatic temperature control)
  • Data Presentation
    • Temporary Displays - VDU, LCD Display (Example: showing a price on a display)
    • Permanent Display - Printer (Example: a receipt)
    • Electrical/Mechanical Output - Actuator (Example: Sending credit card data from a bank to a cash machine)

Design Data Structures[edit | edit source]

Hardware Components[edit | edit source]

Suitable Interface[edit | edit source]

The major two user interfaces are command line interfaces (CLI) and graphical user interfaces (GUI).

CLI's are much easier to implement and use less memory, however there is a much greater learning curve, yet long-term users may find them quicker than other interfaces.

GUI's are much more complex to implement and use more memory, they also require a mouse. Yet, icons make it easier to remember commands and these are grouped in menus. There is a much smaller learning curve. GUI's can also be referred to as 'WIMP' (Windows, Icons, Menus, Pointers)

System Flowchart[edit | edit source]

Usually X-shaped with inputs at the top of the X, processing in the middle and outputs at the bottom. Some of the shapes are parallelogram for input/output, trapezium for manual input, square for process, rectangle with curved bottom for document, and cylinder for disk storage.

Construct System Flowchart[edit | edit source]