A1.3 Operating systems and control systems

Question 1

Role of an operating system

Answer 1

Abstracts hardware complexity and manages system resources (CPU, memory, I/O, storage, devices) to provide a stable platform for applications.

Question 2

Kernel vs user-space

Answer 2

Kernel performs privileged operations and manages hardware; user-space runs applications without direct hardware access.

Question 3

System call

Answer 3

Mechanism by which user programs request services from the kernel (e.g., open file, allocate memory).

Question 4

Main functions of an operating system

Answer 4

Process management, memory management, file system, device management, scheduling, security, GUI, virtualization, networking, accounting.

Question 5

User interface vs programming interface

Answer 5

GUI/CLI are interfaces for users
APIs/system calls are interfaces for programs.

Question 6

Process states

Answer 6

New, Ready, Running, Waiting (Blocked), Terminated - typical process lifecycle.

Question 7

Context switch

Answer 7

Saving and restoring CPU state (registers, program counter) when switching processes; introduces overhead.

Question 8

Preemption

Answer 8

Interrupting a running process to run a higher-priority one; essential for RTOS and fairness.

Question 9

Purpose of process scheduling

Answer 9

Optimize CPU usage, ensure responsiveness, meet deadlines (in RTOS) and fairness between processes.

Question 10

FCFS (First-Come First-Served) characteristics

Answer 10

Simple: tasks served in arrival order; drawback: convoy effect (long job blocks short ones).

Question 11

Round Robin characteristics

Answer 11

Time-sliced scheduling (quantum) for fairness; quantum size affects latency and context-switch overhead.

Question 12

Priority scheduling

Answer 12

Higher-priority processes run before lower-priority ones; risk of starvation for low-priority processes.

Question 13

Multilevel queue scheduling

Answer 13

Processes are divided into queues (e.g., interactive, batch), each with its own policy and priority level between queues.

Question 14

EDF (Earliest Deadline First)

Answer 14

Dynamic scheduling for real-time systems: job with closest deadline runs first.

Question 15

RMS (Rate Monotonic Scheduling)

Answer 15

Static priority scheduling for periodic tasks: shorter period = higher priority, with schedulability guarantees under assumptions.

Question 16

Comparing Round Robin vs Priority

Answer 16

RR: fairness and responsiveness for interactive tasks
Priority: better for time-critical tasks but requires starvation mitigation

Question 17

Convoy effect explanation

Answer 17

A long job at the head of the queue delays many short tasks, reducing responsiveness.

Question 18

What is an interrupt?

Answer 18

Hardware or software signal that temporarily halts CPU execution to run an interrupt handler.

Question 19

Advantages of interrupts

Answer 19

Lower CPU overhead, immediate reaction to events, suitable for I/O and real-time tasks.

Question 20

Polling - what and when

Answer 20

CPU repeatedly checks device status; simple but CPU-intensive; used when interrupts are unavailable or polling cost is acceptable.

Question 21

Polling vs interrupts comparison

Answer 21

Polling: simple but wastes CPU
Interrupts: efficient and responsive but more complex to handle and manage context switching

Question 22

Virtual memory concept

Answer 22

Mapping logical addresses to physical memory using pages, providing isolation and ability to use disk as extension of RAM.

Question 23

Paging vs segmentation

Answer 23

Paging: fixed-size pages
Segmentation: logical segments of variable length (code, data, stack)

Question 24

Swapping and thrashing

Answer 24

Swapping: moving processes between RAM and disk
Thrashing: excessive swapping causing low throughput and high overhead

Question 25

Memory allocation in RTOS constraints

Answer 25

Avoid unpredictable dynamic allocation; use static pools and deterministic algorithms to prevent jitter.

Question 26

Device drivers role

Answer 26

Bridge between hardware and OS: configure devices, handle interrupts, perform data transfer, and expose safe APIs.

Question 27

Race condition

Answer 27

Incorrect program behavior due to uncontrolled ordering of operations on shared data; requires synchronization.

Question 28

Mutual exclusion

Answer 28

Mechanisms (mutexes, semaphores) to ensure only one thread/process executes a critical section at a time.

Question 29

Benefits of multitasking

Answer 29

Better CPU utilization, responsiveness, ability to run multiple applications concurrently.

Question 30

Challenges of multitasking

Answer 30

Synchronization, security, memory management, priority inversion, deadlocks, determinism in RTOS.

Question 31

Resource management in OS

Answer 31

Allocate and free resources, accounting, policy enforcement, fairness and limits.

Question 32

What is an RTOS?

Answer 32

A Real-Time Operating System designed to provide predictable, deterministic responses to events within strict timing constraints.

Question 33

Determinism and jitter

Answer 33

Determinism: predictable response times; Jitter: variability in response times which degrades predictability.

Question 34

Hard vs soft real-time

Answer 34

Hard: missing a deadline is catastrophic (e.g., airbag) Soft: occasional misses degrade quality but are tolerable (e.g., video streaming).

Question 35

Priority-based preemptive scheduling in RTOS

Answer 35

Higher-priority tasks preempt lower ones to ensure critical tasks meet deadlines.

Question 36

Timers and clocks in RTOS

Answer 36

Hardware timers schedule periodic tasks and measure deadlines; essential for deterministic behavior.

Question 37

Control system components

Answer 37

Setpoint (desired value), sensor (measurement), comparator, controller, actuator, process output, feedback path.

Question 38

Open-loop control

Answer 38

No feedback; controller sends commands without measuring the output. Simple but cannot correct disturbances.

Question 39

Closed-loop control

Answer 39

Uses feedback to compare output with setpoint and adjusts control signals to minimize error.

Question 40

Examples of open-loop and closed-loop systems

Answer 40

Open-loop: washing machine cycle based on time. Closed-loop: thermostat controlling room temperature.

Question 41

Role of feedback

Answer 41

Reduces error between setpoint and output and improves robustness to disturbances.

Question 42

Sensor function

Answer 42

Convert a physical quantity (temperature, pressure) into an electrical signal for measurement.

Question 43

Factors affecting control stability

Answer 43

Loop gain, delays, sampling rate, and process dynamics; high gain or delays can destabilize.

Question 44

Effects of delay and jitter

Answer 44

Delays and variable timing can introduce phase lag and oscillations, reducing stability and accuracy.

Question 45

PLC (Programmable Logic Controller) - purpose

Answer 45

Ruggedized controller for industrial automation; programmable, reliable, tolerant to harsh environments.

Question 46

SCADA - role

Answer 46

Supervisory control and data acquisition: gather telemetry, visualize processes, and control remote systems.

Question 47

OS-control integration requirements

Answer 47

Predictable scheduling, bounded interrupt latencies, deterministic memory allocation, security and redundancy.

Question 48

Example integration problem - OS delays

Answer 48

OS-induced delay in interrupt handler causes missed safety event (e.g., collision sensor) leading to unsafe behavior.

Question 49

How OS can improve control precision

Answer 49

Priority critical tasks, minimize jitter, use DMA, hardware timers, and reduce dynamic allocation in critical paths.

Question 50

OS security in ICS - methods

Answer 50

Network segmentation, authentication, encryption, monitoring, redundancy, and secure update mechanisms.

Question 51

Consequences of poor security in ICS

Answer 51

Sabotage, process disruption, equipment damage, safety hazards, and financial loss.

Question 52

RTOS in autonomous vehicles - example

Answer 52

RTOS ensures deterministic sensor handling (lidar, radar), motor control, and emergency braking within deadlines.

Question 53

Compare open-loop vs closed-loop (short)

Answer 53

Open-loop: simple and cheap but cannot correct disturbances. Closed-loop: accurate and robust but more complex and costly.

Question 54

Compare GPOS vs RTOS (short)

Answer 54

GPOS: designed for throughput and user experience; RTOS: designed for determinism and meeting deadlines.

Question 55

Quick definition: Jitter

Answer 55

Variation in timing of events or responses that degrades deterministic behavior.