Flashcards · 9618 · A Level Topic 16

System Software (A Level) flashcards

10 cards on A Level Topic 16, subtopics 16.1 to 16.2. Pick a subtopic or study them all.

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What is the difference between a program and a process?: A program is the code stored on disk. A process is a program that has been loaded into memory and is being executed.
What are the three main process states?: Running (using the processor), ready (waiting for its turn) and blocked (waiting for an event such as input/output to finish).
Name four process scheduling routines.: First come first served, shortest job first, shortest remaining time first, and round robin (each process gets a fixed time slice in turn).
What is the difference between paging and segmentation?: Paging: memory is split into fixed-size pages and frames. Segmentation: memory is split into variable-size segments matching logical parts of a program.
What is virtual memory, and what is disk thrashing?: Virtual memory uses secondary storage as an extension of RAM, swapping pages in and out. Disk thrashing happens when pages are swapped so often that the computer spends more time swapping than processing.

What are the stages of compilation?: Lexical analysis, syntax analysis, code generation and optimisation.
What happens in lexical analysis?: White space and comments are removed, and the code is split into tokens; identifiers are added to the symbol table.
What happens in syntax analysis?: The tokens are parsed and checked against the grammar of the language; syntax errors are reported.
What are BNF and syntax diagrams used for?: To define the grammar of a language. Backus–Naur Form uses rules such as ⟨digit⟩ ::= 0|1|…|9 and can define items recursively; syntax diagrams show the same rules graphically.
What is Reverse Polish Notation (RPN)?: A way of writing expressions with the operator after its operands, so no brackets are needed: (a + b) × c becomes a b + c ×. It is evaluated with a stack.