Topic 3 of 8 · Form 5
System software
Manages memory (paging, segmentation, virtual memory), processes (scheduling: round robin, shortest job first, first come first served, priority), files, input/output, security and the user interface.
Notes for this topic 1 file, in order
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The operating system
Manages memory (paging, segmentation, virtual memory), processes (scheduling: round robin, shortest job first, first come first served, priority), files, input/output, security and the user interface.
- Process states: ready, running, blocked.
- Virtual memory uses secondary storage as an extension of RAM; excessive swapping causes thrashing.
Utility software
Antivirus, defragmentation, backup, compression and disk formatting.
Translators
- Assembler: assembly to machine code.
- Compiler: translates the whole program into object code; fast execution; errors reported after compilation; source code not needed to run.
- Interpreter: translates and executes line by line; easier debugging; slower; source code needed.
- Intermediate code (bytecode) for portability (Java virtual machine).
Stages of compilation
Lexical analysis (tokens, removing comments and white space, symbol table), syntax analysis (checking grammar, parse tree), code generation, and optimisation.
Libraries and linkers
Library routines are pre-written, tested code; a linker combines modules; a loader places code in memory.
Grammar
Backus–Naur Form (BNF) and syntax diagrams define language rules.
Check yourself
- Name the four stages of compilation.
- What is thrashing?
- Give one advantage of an interpreter during development.
Show answers
- Lexical analysis, syntax analysis, code generation, optimisation.
- Excessive swapping of pages between RAM and disk, slowing the computer greatly.
- Errors are shown line by line, making debugging easier.
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