Memory Management Questions and Answers

Answer: A

Correct answer: each process

Every process has its own page table, which is what makes its address space private: the same page number in two processes maps to different frames.

Answer: C

Correct answer: either low or high memory (depending on the location of interrupt vector)

The operating system is placed at whichever end of memory the interrupt vector occupies, since the vector must be reachable and is fixed by the hardware. On most machines that is low memory, but the principle rather than the address is what matters.

Answer: A

Correct answer: each process is contained in a single contiguous section of memory

Contiguous allocation means each process occupies one unbroken run of addresses. That is what makes it simple - a base and a limit describe the whole process - and also what causes external fragmentation.

Answer: C

Correct answer: to protect the address spaces of processes

The relocation register holds the smallest physical address a process may use and the limit register the size of its range. Every address is checked against the limit and then added to the relocation value, so a process cannot reach outside its own space.

Answer: A

Correct answer: less than

A logical address is an offset from the start of the process, so it is valid only while it is less than the limit. An address equal to the limit is the first one beyond the region.

Answer: D

Correct answer: A program may fail if the required library version is changed or missing

With dynamic linking the library is not bound into the executable but located at run time, so a program depends on finding a compatible version present on the system. If the library is missing, moved or replaced by an incompatible version, the program fails to run - the difficulty known informally as dependency hell. Its advantages are substantial, which is why it is universal. Executables are far smaller, since library code is not duplicated into each. One copy of a library in memory serves every process using it, mapped into each address space. And a library can be patched - for a security fix, say - and every program benefits without relinking. Version management is handled by numbering, so several versions can coexist and each program binds to the one it needs. Static linking avoids the dependency entirely by copying the library in, at the cost of size and of losing the shared updates. That is why it is still chosen for self-contained or embedded software.

Answer: C

Correct answer: hardware that translates logical addresses into physical addresses

The MMU is hardware, part of the processor, that translates every logical address the CPU generates into a physical address before it reaches memory. It must be hardware because the translation happens on every single memory reference, and software could not possibly keep up. In the simplest scheme it adds a relocation register and checks a limit; in a paged system it walks the page table and consults the TLB. It also enforces protection on the same pass, checking the valid bit and the permission bits and trapping to the operating system on a violation - which costs nothing extra, since the entry has to be read for translation anyway. The operating system’s role is to set up the structures the MMU uses - page tables, base and limit registers - and to handle the traps it raises. The division of labour is exact: policy in software, mechanism in hardware. A system without an MMU cannot support virtual memory or genuine process isolation, which is why simple embedded controllers run everything in one address space.

Answer: C

Correct answer: allocates the first free block large enough to satisfy the request

First Fit scans the list of free blocks from the beginning and takes the first one large enough. It is the fastest of the placement strategies because the search stops as soon as a candidate is found. Best Fit searches the whole list for the smallest adequate block, on the reasoning that it wastes least - but it must examine every block, and it leaves behind a scatter of tiny remainders too small to use, so it often produces worse fragmentation in practice. Worst Fit takes the largest block, leaving a remainder big enough to be useful; it performs poorly in most studies. Simulation generally finds First Fit and Best Fit better than Worst Fit in both storage utilisation and time, with First Fit faster. All three apply to contiguous allocation and all three suffer external fragmentation, which is what paging was introduced to remove. A variant, Next Fit, resumes the search where the previous one ended rather than starting over.

Answer: A

Correct answer: exactly one process

With fixed partitions each partition holds one process, and the unused space inside the partition is wasted - which is exactly internal fragmentation.

Answer: A

Correct answer: the number of partitions

One process per partition means the number of processes that can be in memory at once, and so the degree of multiprogramming, cannot exceed the number of partitions.