B CompE Bachelor of Computer Engineering Bachelor of Computer Engineering Operating System 5

Question 1

What is the purpose of a 'context switch' in a multitasking OS?

Accepted Answer

Saving one process's CPU state and restoring another's to allow time-sharing

Answer

A context switch saves the current process's registers, program counter, and stack pointer, then restores the saved state of the next scheduled process.

Question 2

Which I/O technique allows a device to transfer data directly to/from memory without CPU involvement on every byte?

Accepted Answer

Direct Memory Access (DMA)

Answer

DMA offloads bulk data transfers to a dedicated controller, freeing the CPU to execute other instructions while the transfer completes.

Question 3

In a two-level page table, why is the outer (directory) page table needed?

Accepted Answer

To avoid allocating a large contiguous page table for sparse address spaces

Answer

A two-level page table splits the virtual address into two indices, allowing unallocated portions of the address space to skip allocating second-level tables entirely.

Question 4

Which RAID level mirrors data across two disks, providing fault tolerance but halving usable capacity?

Accepted Answer

RAID 1

Answer

RAID 1 writes identical data to two disks simultaneously; if one fails, the other contains a complete copy, but only 50% of total disk capacity is usable.

Question 5

What mechanism does the OS use to protect the kernel from direct access by user-mode programs?

Accepted Answer

Privileged (ring) CPU modes enforced by hardware

Answer

Modern CPUs implement privilege rings (typically ring 0 for kernel, ring 3 for user), and the hardware blocks user-mode code from executing privileged instructions.

B CompE Bachelor of Computer Engineering Practice Test

B CompE Bachelor of Computer Engineering Practice Test

B CompE Bachelor of Computer Engineering Bachelor of Computer Engineering Operating System 5