Memory Management Questions and Answers

Answer: C

Correct answer: context – switch

Each process has its own page table, so switching processes means reloading the page table registers or the base register, and flushing the TLB. That work is added to every context switch.

Answer: A

Correct answer: a segment number & offset

A segmentation address names which segment and how far into it. Unlike paging, the division is supplied by the program rather than imposed by the hardware, because segments correspond to logical units such as code, stack and data.

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: A

Correct answer: cannot be done

Compaction moves a process to a different physical address, so its addresses must be recomputed. If relocation was fixed at assembly or load time the addresses are already bound and cannot be changed, so the process cannot be moved.

Answer: B

Correct answer: page table base register

The page table base register holds the address of the current process's page table, so a context switch need only reload that one register.

Answer: D

Correct answer: slowed by a factor of 2

With the table in memory, each reference needs two accesses: one to read the page table entry and one to reach the datum. The effective access time is therefore doubled, which is precisely why the TLB exists.

Answer: A

Correct answer: memory management unit

The MMU is the hardware that performs the translation on every reference, using the page or segment tables. Doing it in hardware is what makes virtual memory affordable.

Answer: D

Correct answer: Base and limit registers

The base register holds the smallest physical address the process may use, and the limit register holds the size of its range. Every address generated is checked: it must be less than the limit, and the base is then added to give the physical address. The check is performed by hardware on every reference, so it costs nothing in time, and any violation traps to the operating system as an addressing error. The registers can be loaded only by a privileged instruction, executable in kernel mode alone. That is what makes the protection genuine: a user program cannot alter the bounds of its own confinement. The distinction between user and kernel mode exists largely to support arrangements of this kind. The scheme also supplies relocation, since changing the base register moves the process without altering any address within it - which is what makes swapping and compaction possible. Paging generalises the idea, replacing the single register pair with a page table.

Answer: B

Correct answer: source program

The program as the programmer writes it is the source; what the translator produces from it is the object program or machine code.

Answer: A

Correct answer: local variable

A variable declared inside a subroutine and visible only there is local. Confining it prevents the routine from disturbing anything outside it.