WGU D686 (OA) Operating Systems for
Computer Scientists STUDY GUIDE 2026
COMPLETE QUESTIONS WITH CORRECT
DETAILED ANSWERS || 100% GUARANTEED
PASS <RECENT VERSION>
Module 1: Introduction & System Structures
1. Q: What is the main purpose of an operating system?
A: To act as an intermediary between the user/hardware, providing an environment for
program execution and managing computer resources (CPU, memory, storage, I/O)
efficiently and securely.
2. Q: Differentiate between kernel mode and user mode.
A: The CPU runs in kernel mode (supervisor mode) to execute privileged OS instructions
that directly control hardware. In user mode, applications run with restricted access,
preventing them from damaging the system. Mode switching is handled via system calls.
3. Q: What is a system call? Provide an example.
A: A system call is a programming interface for a process to request a service from the
OS kernel (e.g., open(), fork(), write()). Example: A program calls read() to access a file,
which triggers a context switch to the kernel to perform the disk I/O.
Module 2: Process Management
4. Q: What is the difference between a process and a thread?
A: A process is an independent program in execution with its own memory space (code,
data, heap, stack). A thread is a lightweight unit of execution within a process; threads of
the same process share memory and resources but have their own stack and register
state.
5. Q: Describe the possible states in a process lifecycle (process state diagram).
A: New -> Ready -> Running -> Waiting/Blocked -> Terminated. A running process
moves to Waiting for I/O, then back to Ready. The scheduler moves a Ready process
to Running.
, 6. Q: What is Process Control Block (PCB)?
A: A data structure in the OS kernel that stores all information about a process (process
state, PC, CPU registers, memory limits, open files, etc.). It is essential for context
switching.
Module 3: CPU Scheduling
7. Q: What is the goal of CPU scheduling?
A: To maximize CPU utilization and system throughput while minimizing wait time,
response time, and turnaround time for processes.
8. Q: Compare Shortest-Job-First (SJF) and Round Robin (RR) scheduling.
A: SJF is optimal for minimizing average wait time but requires accurate burst time
knowledge and can cause starvation. Round Robin uses a time quantum; it's fair and
good for time-sharing systems, but average wait time can be high with poor quantum
choice.
Module 4: Synchronization & Deadlocks
9. Q: What is a race condition?
A: A situation where the outcome of concurrent processes/threads depends on the non-
deterministic order of execution, leading to inconsistent data when accessing shared
resources without proper synchronization.
10. Q: What are the four necessary conditions for deadlock (Coffman conditions)?
A: 1) Mutual Exclusion, 2) Hold and Wait, 3) No Preemption, 4) Circular Wait. All four
must hold for a deadlock to occur.
Module 5: Memory Management
11. Q: What is the difference between logical (virtual) and physical addresses?
A: A logical address is generated by the CPU and used by a process; it is virtual.
A physical address is the actual location in main memory. The Memory Management
Unit (MMU) translates logical to physical addresses at runtime.
12. Q: What is paging? How does it solve fragmentation?
A: Paging divides physical memory into fixed-size frames and logical memory into same-
size pages. It allows a process's non-contiguous pages to be stored in non-contiguous
frames, eliminating external fragmentation (but causing internal fragmentation).
Module 6: Virtual Memory
Computer Scientists STUDY GUIDE 2026
COMPLETE QUESTIONS WITH CORRECT
DETAILED ANSWERS || 100% GUARANTEED
PASS <RECENT VERSION>
Module 1: Introduction & System Structures
1. Q: What is the main purpose of an operating system?
A: To act as an intermediary between the user/hardware, providing an environment for
program execution and managing computer resources (CPU, memory, storage, I/O)
efficiently and securely.
2. Q: Differentiate between kernel mode and user mode.
A: The CPU runs in kernel mode (supervisor mode) to execute privileged OS instructions
that directly control hardware. In user mode, applications run with restricted access,
preventing them from damaging the system. Mode switching is handled via system calls.
3. Q: What is a system call? Provide an example.
A: A system call is a programming interface for a process to request a service from the
OS kernel (e.g., open(), fork(), write()). Example: A program calls read() to access a file,
which triggers a context switch to the kernel to perform the disk I/O.
Module 2: Process Management
4. Q: What is the difference between a process and a thread?
A: A process is an independent program in execution with its own memory space (code,
data, heap, stack). A thread is a lightweight unit of execution within a process; threads of
the same process share memory and resources but have their own stack and register
state.
5. Q: Describe the possible states in a process lifecycle (process state diagram).
A: New -> Ready -> Running -> Waiting/Blocked -> Terminated. A running process
moves to Waiting for I/O, then back to Ready. The scheduler moves a Ready process
to Running.
, 6. Q: What is Process Control Block (PCB)?
A: A data structure in the OS kernel that stores all information about a process (process
state, PC, CPU registers, memory limits, open files, etc.). It is essential for context
switching.
Module 3: CPU Scheduling
7. Q: What is the goal of CPU scheduling?
A: To maximize CPU utilization and system throughput while minimizing wait time,
response time, and turnaround time for processes.
8. Q: Compare Shortest-Job-First (SJF) and Round Robin (RR) scheduling.
A: SJF is optimal for minimizing average wait time but requires accurate burst time
knowledge and can cause starvation. Round Robin uses a time quantum; it's fair and
good for time-sharing systems, but average wait time can be high with poor quantum
choice.
Module 4: Synchronization & Deadlocks
9. Q: What is a race condition?
A: A situation where the outcome of concurrent processes/threads depends on the non-
deterministic order of execution, leading to inconsistent data when accessing shared
resources without proper synchronization.
10. Q: What are the four necessary conditions for deadlock (Coffman conditions)?
A: 1) Mutual Exclusion, 2) Hold and Wait, 3) No Preemption, 4) Circular Wait. All four
must hold for a deadlock to occur.
Module 5: Memory Management
11. Q: What is the difference between logical (virtual) and physical addresses?
A: A logical address is generated by the CPU and used by a process; it is virtual.
A physical address is the actual location in main memory. The Memory Management
Unit (MMU) translates logical to physical addresses at runtime.
12. Q: What is paging? How does it solve fragmentation?
A: Paging divides physical memory into fixed-size frames and logical memory into same-
size pages. It allows a process's non-contiguous pages to be stored in non-contiguous
frames, eliminating external fragmentation (but causing internal fragmentation).
Module 6: Virtual Memory
