CP1300 Software Layers

Software Generation

• Software follows a software life cycle.
  • Problem Analysis and Specification
  • Solution Design
  • Algorithm
  • Implementation
  • Compilation
  • Execution

• Compilation
  • Translates source code into machine code
  • Produces an executable binary file (of machine code instructions)

• Execution
  • Executable binary is loaded into main memory, and then run
  • Hardware follows the Fetch Decode Execute Cycle to run a program

Software Layers

• The Layers
  • Application software
  • System software
  • Operating system
  • Device drivers
  • Microcode
  • Hardware
  • Application actions pass through the layers to the hardware

• Application Software
  • Uppermost software layer
  • Where normal computer/user interaction occurs
  • Word processing, email, internet, and so on...
  • Designed to be powerful but easy to use
  • Most have GUI or simple command-line interfaces

• System Software
  • Common activities that high level applications need to do, e.g., printing
  • Library routines and common tools that hide the operating system from applications

• Operating System
  • Programs and routines that control all accesses to hardware
  • Higher levels are protected from any issues
    • Multiple users
    • Multiple requests for the same resource
    • Access control
  • When the OS determines its safe to proceed, direct calls to device drivers and microcode are performed

• Device Drivers
  • Device drivers are very low level instructions to a device (e.g., the printer, or the hard drive)

• Microcode
  • Microcode are very low level, and very specialised instructions to the computer (the CPU, memory)
  • Have nearly one-to-one relationships with the hardware

• Hardware
  • Digital logic components (gates, ICs, and so on)
  • Physical devices
  • ICs (e.g., CPU) are typically 'programmed' during mass manufacturing

Self assessments

• Software Development
• Software Layers

Tutorial Questions

• Software Layers (Answers)

Exam style questions

1. What are the stages in software generation?
2. What does a compiler do?
3. Are compilers machine specific? If so, why?
4. What is executable code?
5. How is an executable 'executed' on a computer?
6. What are software layers for?
7. Draw a diagram of the software layers and hardware.
8. True/False: does each layer depend on the one(s) below it?
9. State the layer that directly handles the following:
   • a word processing application
   • a routine that controls exactly what a particular device does
   • a generic routine to print data to a printer
   • routines to resolve access to a system resource
10. Make a list of all the input-only, output-only, and input&output device that you can think of.