Computer Operating System Questions and Answers

Answer: A

Correct answer: actually schedules the tasks into the processor

The scheduler decides which process should run next; the dispatcher is the module that carries that decision out - switching context, restoring the chosen process’s registers, and handing it the processor. It is on the critical path of every context switch, so its speed matters.

Answer: A

Correct answer: reenterable

A reentrant program keeps no modifiable data in its own code area, so one copy in memory can be executing on behalf of several users at once, each with its own stack and work area. That is exactly what is wanted of a compiler or an editor on a shared system.

Answer: D

Correct answer: CP/M

When the IBM PC appeared in 1981 the dominant operating system for microcomputers was Digital Research’s CP/M, which ran on the 8-bit 8080 and Z80 machines that made up most of the market. PC-DOS shipped with the new machine and displaced it over the following years.

Answer: D

Correct answer: 128

The virtual address space is \( 2^{16} \) bytes and each page holds \( 0.5\ \text{KB} = 512 = 2^9 \) bytes, so the number of pages is \[ \frac{2^{16}}{2^{9}} = 2^{7} = 128 \] - the top 7 bits of the address are the page number and the low 9 bits the offset within it.

Answer: A

Correct answer: Terminal table

The terminal table holds the language’s own fixed symbols - keywords, operators and punctuation - one entry for each terminal symbol of the grammar. It is permanent because it is identical for every compilation, whereas the identifier and literal tables are built anew from each source program.

Answer: A

Correct answer: to recognize the major constructs of the language and to call the appropriate action routines

The syntax phase takes the token stream from the lexical phase and parses it against the grammar, recognising declarations, expressions and statements, and calling the action routine that handles each construct as it is identified. Building the symbol, literal and uniform symbol tables is lexical-phase work.

Answer: C

Correct answer: allows each program in turn to use the memory

Swapping moves a whole process out to backing store and brings another in, so the processes take turns occupying memory rather than sharing it at the same instant. It is the coarsest form of memory management, and it is what paging refines by moving pages rather than whole processes.

Answer: C

Correct answer: Scan

The SCAN algorithm, often called the elevator algorithm, sweeps the arm steadily from one end of the disk to the other and back, serving every request it passes on the way. It avoids the starvation of far-out requests that shortest-seek-time-first can cause, while still moving far less than first-come-first-served.

Answer: B

Correct answer: a system software

A translator - a compiler, assembler or interpreter - serves the machine and the programming process rather than an end user’s task, which is what makes it system software. Application software is what the user runs to do the job they actually came for.

Answer: B

Correct answer: is mostly used by financial networks

Encryption is used most heavily where the value of intercepted data is highest and the legal obligation strongest - banking and payment networks, which encrypt transactions, PINs and balances end to end. Any private installation may use it, and data crossing any network can certainly be intercepted.