Computer Software: System Software, Operating Systems, Utilities and Applications
Computer software covers the programs that make hardware usable: system software that manages the machine and application software that does the user's work. The exam tests classification, operating-system functions, the difference between translators, and justified choices between off-the-shelf and bespoke software.
System software
System software includes the operating system, utilities, device drivers, firmware and language translators. An operating system provides process management (scheduling, multitasking), memory management (allocation, virtual memory), file management, device management through drivers, a user interface (GUI or command line), and security (accounts, passwords, access rights). Types include single-user, multi-user, batch, real-time and distributed systems; a real-time operating system must respond within a guaranteed time, which is why it controls aircraft and industrial plant. Utilities are maintenance programs: backup, antivirus, disk cleanup, compression, defragmentation and file managers. Firmware is software stored in ROM or flash - the BIOS/UEFI that starts the machine - and counts as system software. Translators: an assembler converts assembly language into machine code; a compiler translates the whole high-level program into object code before it runs; an interpreter translates and executes one statement at a time.
Application software
General-purpose packages (word processors, spreadsheets, databases, browsers, graphics) versus special-purpose packages (payroll, stock control, CAD, point-of-sale). Off-the-shelf software is cheaper, immediately available, well tested and supported, but may not match the organisation's processes; bespoke software fits exactly and can give competitive advantage, but costs more, takes longer and needs thorough testing and maintenance.
Worked example
A loop body must run 5,000 times. With an interpreter the statement is translated on every pass, so roughly 5,000 translations occur and execution is slower, but an error message points to the line where it happened. A compiler translates once, produces object code that runs fast, reports errors only after scanning the whole program, and needs a separate version for each processor type. The reasoning is translation once versus many times.
Traps
Do not class firmware as application software; utilities are maintenance tools, not productivity packages; defragmentation applies to magnetic disks, not SSDs; and a compiler producing an executable is not the same as a compiler running the program.