Memory Management Questions and Answers

Answer: A

Correct answer: translate a logical page number into a physical frame number

A page table maps each logical page of a process to the physical frame holding it. A logical address is split into a page number and an offset; the page number indexes the table to give a frame number, and the offset is carried across unchanged. That indirection is what makes paging work. A process’s pages need not be contiguous in physical memory, so external fragmentation disappears, and each process gets its own address space isolated from every other. Its cost is an extra memory access for every reference, which would halve performance. The remedy is the translation lookaside buffer, a small associative cache of recent translations; hit rates above 90 per cent bring the average close to a single access. Each entry also carries protection and status bits - valid or invalid, read-only, and a modified or dirty bit recording whether the page must be written back when replaced. For large address spaces the table is itself paged, giving multilevel page tables.

Answer: A

Correct answer: Fixed partitioning

Fixed partitioning divides memory once, at system generation, so the operating system need only record which partitions are occupied. It is the simplest scheme and the cheapest to run; the price is internal fragmentation and a fixed limit on the degree of multiprogramming.

Answer: A

Correct answer: a page is a fixed-size physical division while a segment is a variable-size logical one

A page is a fixed-size division imposed by the system with no regard to program structure; a segment is a variable-size division corresponding to a logical unit of the program - code, data, stack, a procedure, an array. Everything else follows from that. Paging is invisible to the programmer, since the division is arbitrary; segmentation reflects the programmer’s own view. Paging suffers internal fragmentation and none external; segmentation suffers external and none internal. A paged address is one number split into page and offset; a segmented address is genuinely two-dimensional, a segment number and an offset. Segmentation makes protection and sharing natural, since a whole segment can be marked read-only and a shared library is one segment mapped into several processes. Paging can share too - the fourth option is wrong - but a page has no logical meaning, so the unit is arbitrary. Many real architectures combine both, dividing a program into segments and then paging each segment.

Answer: B

Correct answer: Modem

A telephone line carries an analogue signal, so a modem is needed to convert the computer's digital data for transmission and back again on arrival.

Answer: A

Correct answer: brackets

In COMAL a procedure's parameters follow its name in brackets, both where it is defined and where it is called, which is what binds each argument to its parameter.

Answer: B

Correct answer: NULL

When new cannot obtain the memory it returns a null pointer in the traditional form, and in standard C++ throws std::bad_alloc unless the nothrow form is used. Testing the returned pointer is what the traditional form requires.

Answer: C

Correct answer: It is a type of conversation that takes place on a computer network in real time

Chat is live typed conversation: what one person types appears on the other's screen at once. A discussion area where messages are posted and read later is a forum, and uploading files is FTP.

Answer: A

Correct answer: loop

Statements repeated until a condition is met form a loop. A case statement chooses among alternatives once rather than repeating.

Answer: C

Correct answer: free hole from a set of available holes

First fit, best fit and worst fit are placement strategies: given a request and a list of free holes, each chooses a different hole. First fit takes the first large enough, best fit the smallest large enough, worst fit the largest.

Answer: A

Correct answer: internal fragmentation occurs

Memory allocated to a process but not used by it is internal fragmentation - the waste lies inside the allocation. External fragmentation is waste between allocations.