Computer Operating System Questions and Answers

Answer: A

Correct answer: to improve disk performance

A block or buffer cache keeps recently used disk blocks in main memory, so a repeated read is answered without touching the disk and writes can be gathered and deferred. Since a memory access is several orders of magnitude faster than a disk access, this is where most of the gain in file system performance comes from.

Answer: B

Correct answer: internal fragmentation is increased with small pages

Internal fragmentation is the unused part of the last page of an allocation, so it averages half a page - which means small pages reduce it, and the statement is false. The other three are true: small pages need larger page tables, large pages drag in data that will not be used, and large transfers are more efficient.

Answer: B

Correct answer: lexical analysis

Lexical analysis is the first phase: it scans the source character by character and groups the characters into tokens - identifiers, keywords, constants, operators - classifying each. Syntax analysis then takes that stream of tokens and checks it against the grammar of the language.

Answer: B

Correct answer: A decision table is directly understood by the computer

A decision table sets out conditions and the actions that follow from each combination of them, which makes it easy for people to read, check and change - but it is a design document. It must still be translated into a program before a computer can act on it, so that statement is the untrue one.

Answer: A

Correct answer: are legitimate programs that allow unauthorized access

A Trojan horse works precisely because it appears to be a legitimate, useful program: the user installs and runs it willingly, and while it does whatever it advertises it also opens a way in for the attacker. Unlike a virus it does not replicate; its whole method is the disguise.

Answer: A

Correct answer: 1981

IBM shipped PC-DOS 1.0 with the original IBM Personal Computer in August 1981. Microsoft supplied it, having bought 86-DOS from Seattle Computer Products and adapted it, and sold the same system separately as MS-DOS.

Answer: D

Correct answer: faster

A disk beats main memory on every count listed except speed: it keeps its contents without power, holds far more, and costs far less per bit. But an access takes milliseconds against the nanoseconds of memory - a difference of about a million times, which is why data must be brought into memory to be worked on.

Answer: D

Correct answer: all of the above

The producer–consumer problem needs mutual exclusion on the buffer and a way to make the producer wait when it is full and the consumer wait when it is empty. Semaphores provide both directly, event counters do it without mutual exclusion by counting occurrences, and monitors package the buffer with its condition variables. All three solve it.

Answer: B

Correct answer: they are initially stored on disk

These systems are called disk operating systems because the system itself lives on disk and is loaded from there when the machine starts, rather than being held permanently in ROM as the earlier microcomputer monitors were. Managing files on disk was their central new capability.

Answer: D

Correct answer: branches off to the interrupt service routine after completing the current instruction

The processor checks for pending interrupts at the end of each instruction, not in the middle of one - the machine state must be consistent before it can be saved. It then saves the program counter and status, branches to the service routine, and resumes the interrupted program afterwards.