Computer Operating System Questions and Answers

Answer: A

Correct answer: virtual memory is used only in multi-user systems

Virtual memory serves a single-user machine just as well - it lets a program larger than physical memory run and isolates processes from one another - so that statement is untrue. The other three are correct: segmentation leaves external fragmentation, paging leaves internal fragmentation, and segments may themselves be paged.

Answer: B

Correct answer: Specify, to the operating system, the beginning and end of a job in a batch

JCL statements bracket and describe a batch job for the operating system: the JOB statement marks its start and gives the accounting information, EXEC statements name the programs to run, and DD statements describe the data sets they use. JCL declares what is wanted; it does not itself move data or allocate the processor.

Answer: A

Correct answer: is a method of memory allocation by which the program is subdivided into equal portions or pages

Paging divides the address space into fixed-size pages and memory into frames of the same size, so any page can go in any free frame. Because the pieces are all the same size there is no external fragmentation, and a program need not occupy contiguous memory.

Answer: B

Correct answer: Documentation increases the maintenance time and cost

Good documentation reduces maintenance time and cost, because the next person to change the program can understand it instead of rediscovering it - so that statement is the untrue one. The others are correct: documentation should be clear and direct, and it improves understanding of the problem.

Answer: A

Correct answer: allows the programmer to write base registers and displacements explicitly in the source program

The System/370 addresses memory as a base register plus a displacement, and its assembler language lets the programmer write both explicitly - or leave the assembler to supply them from a USING declaration. That control over addressing is characteristic of the language.

Answer: A

Correct answer: allowing jobs to use the processor

Scheduling is deciding which of the ready jobs gets the processor and for how long. It is central to performance - throughput, turnaround and response time all depend on it - it is needed on a uniprocessor precisely because there is only one processor to share, and the policy chosen depends on what the system is for.

Answer: A

Correct answer: preemptive scheduling

Under preemptive scheduling the operating system may take the processor from a process that is still able to run - when its time slice expires or a higher-priority process becomes ready - suspending it temporarily and resuming it later. Non-preemptive scheduling waits for the process to block or finish.

Answer: D

Correct answer: Loading

In an absolute loading scheme the assembler has already fixed the addresses and resolved the references, so the loader has nothing to allocate, relocate or link - it simply places the program at the addresses named and transfers control. Only the loading function remains.

Answer: D

Correct answer: hashing

Hashing computes a storage address directly from the record’s key, so a record can be reached in a single access without consulting an index. Its cost is collisions, when two keys hash to the same address, which must be resolved by chaining or by probing.

Answer: B

Correct answer: 2

Dekker’s algorithm was the first correct software solution to mutual exclusion, and it works for exactly two processes. It combines two intention flags with a turn variable, so that when both want to enter the turn variable breaks the tie and neither can be starved. Generalising it to \( n \) processes needed Dijkstra’s and later Lamport’s work.