CCEA A-Level Software Systems Development

Software falls into two broad groups. **Systems software** runs the computer and provides the services other programs depend on. **Application software** does a job for the user, and **application development software** is the set of tools a programmer uses to build it. ## Systems software The operating system is the main piece of systems software. It manages the processor, memory and storage, runs programs, controls input and output devices through device drivers, and provides the file system. Alongside it sit utility programs (disk tools, backup, anti-virus, compression) and the translators that turn a programmer's code into something the processor can run. ### Managing files The operating system organises stored data as files in a hierarchy of folders. It records each file's name, type (often shown by its extension), size, dates and permissions, and it decides who may read, change or run the file. A program that opens a file asks the operating system to do it, which is why a program can fail with a "file not found" or "access denied" error that has nothing to do with its own logic. Four kinds of file matter in software development. | File type | What it holds | Example | |---|---|---| | Source file | The code a programmer writes, as plain text that a person can read and edit | `Program.cs` | | Binary file | Data stored as raw bytes, not meant to be read as text; it is compact and quick to load | a compiled library, an image, a saved object | | Executable file | A binary…