• 1. System Software e.g. Operating System, Utility programs/Software, and device drivers [2024]

  2. Application Software e.g. spreadsheet, word processor, web browser, etc.

Operating System

• System Software

• An operating system (OS) is a program that, after being initially loaded into the computer by a boot program, manages all of the other application programs in a computer. 

• Users can interact directly with the operating system through a user interface such as a command line Interface (CUI) or a graphical user interface (GUI).

• Ex- Windows, Mac, UNIX, LINUX, etc.

MAJOR FUNCTIONS OF OPERATING SYSTEM  [2018, 2019, 2023, 2024]

• 1. Processor Management: This deals with management of the Central Processing Unit (CPU). The operating system takes care of the allotment of CPU time to different processes

  2. Device Management: The Operating System communicates with hardware and the attached devices and maintains a balance between them and the CPU. 

  3. Spooling: This is a device management technique used for processing of different tasks on the same input/output device. Ex. Printer

  4. Memory management: Allocation and reallocation of memory, prevents two processes accessing the same memory 

  5. peripherals  management: allocates data to buffers, transmits data to hardware and receives data from hardware

  6. File Management: The operating System manages the files, folders and directory systems on a computer. Any data on a computer is stored in the form of files and the operating system keeps information about all of them using File Allocation Table (FAT). 

  7. Other uses include

     • provides a user interface

     • input/output control/handling

     • security

     • Utilities (e.g. copy, save, delete, rename, etc.)

     • load/run software

     • error reporting/handling

INTERRUPT [2018, 2024]

• indicates that something requires the attention of the processor/OS/CPU

• Signal sent to a processor which may cause a break in the execution of the current routine, according to priorities

• Can be Software or Hardware based

• The software in the computer that will receive and manage all interrupt signals: Operating System, Interrupt handler or Interrupt service routine  [2020, 2023]

Software Interrupts

• • 1. Division by 0

    2. Null value

    3. Two processes attempting to access the same memory location

    4. Program request for input

    5. Output required

    6. Data required from Memory

Hardware Interrupts

1. Data Input, E.g. Key pressed on a keyboard, mouse click

2. Error from Hardware, e.g. Printer out of paper, Paper jam in printer

3. Hardware Failure

4. New hardware device connected (Plugging in a device)

Descriptive examples:

An interrupt signal is sent from the printer to the computer in the following cases: [2020]

Paper jam Out of paper Out of toner/ink Buffer full Awaiting input Print complete Printer ready

how interrupts are used when a key is pressed on a keyboard. [2023]

• Key press generates the interrupt

• Interrupt given a priority

• Interrupt is sent to CPU

• Interrupt is placed in a queue

• CPU stops current task to check the queue/service the interrupt ...

•  ... using an interrupt service routine

• If key press is highest priority the interrupt is processed

LOW LEVEL LANGUAGES

• 1. They are closer to the native language of a computer (binary), making them harder for programmers to understand.

  2. They are very close to the hardware and help to write a program at the hardware level (For writing programs, hardware knowledge is a must)-Machine-dependent

  3. Machine language and Assembly language are Low-Level Languages.

  4. Translated program requires less memory

  5. Write codes that can be executed faster

  6. Few programmers write programs in low level assembly language, but it is still used for developing code for specialist hardware, such as device drivers.

  7. Challenging to learn and understand.

HIGH LEVEL LANGUAGES [2019, 2020, 2021]

• 1. Closer to human language

  2. No prior knowledge of Hardware/computer architecture is required (Hardware Independent)

  3. Easier to READ/WRITE/INTERPRET

  4. Easier to debug errors

  5. Portable (can be used in many different platforms)

  6. Code reusability

  7. Built-in functions/libraries (saves time to write programs)

  8. One line of code can carry out multiple commands

  9. Less errors

  10. Examples include: C++, Java, Python, Visual Basic, etc.

A translator is a programming language processor that converts a computer program from one language to another.  

• 1. It takes a program written in source code and converts it into machine code.  It discovers and identifies the error during translation.

  2. Translating the high-level language program input into an equivalent machine language program.

  3. Providing diagnostic messages wherever the programmer violates specification of the high-level language program.

There are 3 different types of translators as follows:

• • • Compiler

    • Interpreter

    • Assembler

ASSEMBLER

• 1. An assembler is a translator used to translate assembly language to machine language (An assembly language use mnemonics codes).

  2. An assembler translates a low-level language, an assembly language to an even lower-level language, which is the machine code.

  3. It is machine dependent, cannot be used in other architecture.

  4. A small change in design can invalidate the whole program.

  5. It is difficult to maintain.

  6. Examples

     • Fortran Assembly Program (FAP)

     • Macro Assembly Program (MAP)

     • Symbolic Optimal Assembly Program (SOAP)

INTERPRETER [2018, 2019, 2024]

(Used while developing and testing the application)

• 1. Interpreter programs are able to read, translate and execute one statement at a time from a high-level language program.

  2. Used during the development of a program.  They make debugging easier as each line of code is analyzed and checked before execution. 

  3. No executable file is produced.  The program is interpreted again from scratch every time you launch it.

  4. It directly executes the operations specified in the source program when the input is given by the user.

  5. It gives better error diagnostics than a compiler.

COMPILER [2018, 2019, 2024]

• 1. Compiler is a translator which is used to convert programs in high-level language to low-level language (or high-level language into machine code (object code))

  2. It translates the entire program at once

  3. Reports the errors in source program encountered during the translation

  4. Once compiled (all in one go), the translated program file can then be directly used by the computer and is independently executable

  5. Compiling may take some time but the translated program can be used again and again without the need for recompilation

Explain why a programmer would make use of both an interpreter and a compiler? [2020]

− To translate the high-level language into low-level language

− Interpreter used whilst writing the program

− Interpreter used to debug code line by line

− Compiler used when program completed

− Compiler used to create separate executable file (so compiler no longer needed)

− If it runs first time in a compiler there are no syntax errors

INTEGRATED/INTERACTIVE DEVELOPMENT ENVIRONMENT (IDE)

• 1. An integrated development environment (IDE) is a software suite that consolidates basic tools required to write, test, and run programs.

  2. Most HLLs offer the use of an IDE

  3. This contains:

     • code editors 

     • run-time environment 

     • translators 

     • error diagnostics 

     • auto-completion 

     • auto-correction

     • prettyprint