Memory Management Questions and Answers

Answer: B

The memory that must be refreshed is DRAM.

Dynamic RAM stores each bit as a charge on a tiny capacitor. The charge leaks away within milliseconds, so the memory controller must read and rewrite every cell periodically, a process called refreshing. DRAM is cheap and dense, which is why it is used as main memory.

Static RAM (SRAM) stores each bit in a flip-flop that holds its state as long as power is supplied, so it needs no refresh; it is used for cache. ROM and PROM are non-volatile and keep their contents without power or refresh.

Answer: B

Cache memory exists to store frequently accessed data for faster retrieval.

Cache is a small, very fast memory placed between the processor and main memory (RAM). It keeps copies of the instructions and data the processor is likely to use again soon, so that most requests can be served without waiting for the slower main memory. This reduces the average memory access time.

Cache is volatile and tiny, so it cannot act as permanent storage for user files, which is the job of secondary storage such as disks. It does not replace main memory or secondary memory when they fill up; virtual memory and storage management deal with that.

Answer: A

Correct answer: operating system

Main memory holds the resident part of the operating system and the user processes together, and the question asks which of them it accommodates. The CPU is not in memory at all, so it cannot be part of the answer.

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: every address generated by the CPU is being checked against the relocation and limit registers

The protection is enforced by hardware on every single memory reference, so no instruction can reach outside its own region however it is written. Being in different address spaces is the consequence of that checking, not the mechanism.

Answer: B

Correct answer: comes and goes as needed

Transient code is loaded when it is wanted and discarded afterwards - device drivers and rarely used routines - so it does not occupy memory permanently. The resident part stays.

Answer: C

Correct answer: changes

Because transient code is loaded and released as it is needed, the amount of memory the operating system occupies goes up and down while programs run. It neither only grows nor only shrinks, which is why the answer is that it changes.