IGCSE Computer science

• System software provides the services that the computer requires, including operating system and utility software
• How the System Software works: allowing instructions to be processed by the CPU to allow word processing software to process. Without systems software the system would be useless
• The Operating System (OS) is the software that manages the computer and controls the computer's hardware.
• The Operating system (OS) also manages files on computer hard drives and control peripherals, like printers and scanners.
• Utility Software is software that is designed to perform a specific task, such as word processing or spreadsheet software.
• Some example of security utilities in Utility Software: anti virus, encryption, and firewall.
• Some examples of Disk organization utilities in Utility Software are: System clean up tools, Disk defragmentation tools, and file compression software, full back up, and incremental back up.
• An interrupter sends signals from hardware or software to the operating system in order to request CPU attention.
• When the OS gets the interrupt, it will suspend its current task and execute an interrupt service routine for the device or application that sent the interrupt.
• Interrupts can also be generated by software, especially when unexpected events occur. In this context they are sometimes known as exceptions. 
• The ability for high-level code to run on multiple different operating systems without change is known as being cross platform.
• Assembly language uses short abbreviations, known as mnemonics
• The program that translates assembly language code into machine code is called assembler.
• IDEs offer auto-completion functions, automatic code formatting and syntax highlighting.
• Length check is when it checks for the number of characters in a field.
• format check is when the format established is correct.
• range check is when it checks for the number entered within a specific range.
• precense check checks that no fields are left in blank.
• Type check checks the data so it is in a specific data type.
• check digits is used to see the accuracy of numbers such as in credit cards.