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

System Design

Parts Of A System

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

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

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

Data in a System

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

Data Capture and Output Presentation

• 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)

Suitable Interface

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

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.