Topic A1.3 - Operating Systems and Control Systems

What are the primary roles of an Operating System?

Manages computer hardware/software, runs applications by providing environment/resources, delivers a User Interface (GUI/CLI), and performs resource management (CPU, memory, storage)[cite: 72].

What does Hardware Management in an OS involve?

Device Control (using device drivers for software to talk to hardware), Resource Allocation (deciding program access to hardware), Interrupt Handling (responding to hardware signals), and Hardware Abstraction (hiding complex hardware details)[cite: 73].

What are the core tasks of OS Memory Management?

Allocation of Memory (assigning RAM to starting programs), Tracking Usage (monitoring free vs occupied memory to prevent overlap), Virtual Memory (extending memory onto disk), and Protection and Isolation (preventing programs from accessing each other's memory)[cite: 74].

How does Virtual Memory function?

When RAM is overloaded, less-used data is temporarily sent to a pagefile in secondary storage (hard disk)[cite: 75]. Data is transferred back to RAM when needed or when space becomes free, though accessing virtual memory takes longer than RAM[cite: 75, 76].

What is Paging in the context of Virtual Memory?

The OS manages virtual memory by transferring fixed-size units called 'pages' of data between RAM and secondary storage, allowing processes to utilize a virtual-address space larger than physical RAM[cite: 76].

What are the main functions of File Management in an OS?

File Organization (structured directories/folders), Storage Management (disk allocation, free space tracking, retrieval), Access Control (read/write/execute permissions), and File Operations (create, open, edit, copy, move, delete)[cite: 77].

What does Security Management encompass in an OS?

Access Control (permissions and user authentication), Data Protection (encryption and process isolation), Threat Prevention (blocking malware and unauthorized access), and Monitoring & Auditing (security logs to track activity and breaches)[cite: 78].

What is the purpose of Accounting in an Operating System?

Resource Tracking (recording CPU time, memory, disk space, and network usage per user/process), Usage Monitoring (activity logs for workload analysis), Billing & Quotas (enforcing limits or charging in shared/cloud systems), and Security & Auditing (logging actions for accountability)[cite: 80].

What is Process Management in an Operating System?

Process Creation & Termination (safely starting and ending processes when programs run) and CPU Scheduling (deciding which processes get CPU time and for how long to maintain system responsiveness)[cite: 81].

What are the 4 main functions of OS Process Management?

1. Process Creation & Termination (starts/ends processes safely); 2. CPU Scheduling (allocates CPU time for responsiveness); 3. Multitasking (switches quickly between processes); 4. Inter-Process Communication (allows processes to share data and coordinate safely)[cite: 82].

What is Virtualization and why is it useful?

The process of creating a virtual version of a resource (computer, OS, or storage) instead of using physical hardware[cite: 83]. Useful for cost savings, better resource utilization, environment isolation, testing, and running multiple OSes[cite: 83].

What is a Hypervisor and what does it do?

A software layer (e.g., VMware, VirtualBox) sitting between physical hardware and Virtual Machines (VMs)[cite: 83, 84]. It trick VMs into seeing dedicated hardware, schedules CPU time, splits physical memory, maps virtual devices to real hardware, and ensures isolation[cite: 84].

What are the pros and cons of Virtualization?

Pros: Efficient resource use, cost savings, easy backup/recovery via snapshots, security isolation, and flexible testing[cite: 85]. Cons: Performance overhead, requires powerful hardware (high RAM/CPU/storage), and complex management[cite: 85].

How does an OS manage Networking?

Manages Network Interfaces (Wi-Fi/Ethernet adapters), Handles Data Packets (breaks data down, adds headers, reassembles), Uses Protocols (TCP/IP for ordered/lossless delivery), and Controls Security & Routing (firewalls and IP routing)[cite: 86].

What constitutes System Integrity in an OS?

1. Correct Functioning (operates as intended without unauthorized changes/errors); 2. Protection Against Tampering (prevents malicious/accidental alterations); 3. Trustworthy Output (delivers reliable, accurate results)[cite: 87].

What are Background Operations and name 3 examples?

Tasks that run "behind the scenes" without showing on screen or interrupting user activity[cite: 88]. Examples: 1. Antivirus scanning; 2. Automatic updates; 3. File indexing[cite: 88].

Why are Background Operations useful in an OS?

1. Monitoring & Security Scans (continuously checks for threats); 2. System Updates & Patching (applies fixes to prevent vulnerabilities); 3. Resource & Process Management (monitors memory/programs to prevent crashes)[cite: 89].

What are the primary duties of OS Device Management?

1. Controls Hardware Access (ensures only authorized processes interact with peripherals); 2. Isolates Faulty Devices (prevents malfunctioning hardware from crashing the system); 3. Enforces Permissions (applies usage policies)[cite: 90].

What are the 4 core features of a Graphical User Interface (GUI)?

1. User Interaction (windows, icons, menus, pointers / WIMP); 2. Visual Feedback (progress bars, notifications, file icons); 3. Ease of Use (user-friendly for non-technical users); 4. Input Handling (mouse clicks, keyboard input, touch gestures)[cite: 91].

What is a Process and its key components?

An instance of a program in execution, comprising its code, instruction pointer, allocated memory space, open file handles, and CPU scheduling info[cite: 92].

What is a Thread and how does multithreading work?

The smallest unit of execution within a process that performs a task and shares memory with other threads in the same process, enabling parallel tasks without process-creation overhead[cite: 93].

What are the 5 common Process States in an OS?

1. New (just created); 2. Ready (waiting for CPU); 3. Running (actively using CPU); 4. Waiting/Blocked (waiting for input/event); 5. Terminated (finished)[cite: 94].

What is CPU Scheduling and why is it necessary?

How the OS manages time-sharing between multiple programs needing the CPU[cite: 95]. It enables multitasking, maximizes CPU utilization, keeps the system responsive, and reduces wait times[cite: 95, 96].

How does First-Come, First-Served (FCFS) Scheduling work and what is its main drawback?

Runs processes uninterrupted in the order they arrive in a queue[cite: 98]. Drawback: Slow processes block faster ones, causing long wait times (known as the "convoy effect")[cite: 98].

How does Round Robin (RR) Scheduling work and what are its trade-offs?

Gives each process a fixed unit of CPU time called a 'quantum'; unfinished processes are paused and sent to the back of the queue[cite: 99]. Trade-off: Too short quantum causes frequent context switching overhead; too long reduces system responsiveness[cite: 99].

What is Multilevel Queue Scheduling and what issue can it cause?

Separates processes into different queues based on characteristics (priority, type, memory needs) with tailored algorithms per queue[cite: 100]. Issue: Lower-priority queues can suffer from starvation if higher queues stay busy[cite: 100].

How does Priority Scheduling work and how does it handle ties?

Assigns each process a priority level and gives CPU time to the highest-priority process first; uses a fallback like FCFS if priorities match[cite: 101]. High-priority streams can cause starvation for low-priority tasks[cite: 101].

What are Slice, Quantum, and Pre-emption in CPU scheduling?

Slice/Quantum: A short, fixed period of CPU time given to a process[cite: 101]. Pre-emption: The act of the OS interrupting a running process to allocate the CPU to another (usually higher-priority) process[cite: 101].

What are Starvation, Burst Time, and Fairness in CPU scheduling?

Starvation: When a low-priority process waits indefinitely because higher-priority processes keep taking the CPU[cite: 101]. Burst Time: Execution time required by a process[cite: 101]. Fairness: Ensuring processes get a reasonable share of CPU time without unfair delays[cite: 101].

What are 4 common examples of Interrupt triggers?

1. Hardware issues (printer jam)[cite: 103]; 2. Software issues (file not found, division by 0, array index out of bounds)[cite: 103]; 3. User intervention (CTRL+ALT+DELETE, Force Quit)[cite: 103]; 4. External events / IO processes (keyboard inputs, mouse clicks, network packets, data transfer completion)[cite: 103].

What is an Interrupt and an Interrupt Service Routine (ISR)?

Interrupt: A signal sent to the CPU by hardware or software indicating an event needs immediate attention[cite: 104]. ISR: Software/routine that executes to handle specific types of interrupts[cite: 105].

State the 5 steps of Interrupt Handling in the Fetch-Execute cycle.

1. Check interrupt priority[cite: 105]; 2. If lower priority, continue F-E cycle; if higher, push current process state onto Stack[cite: 105]; 3. Identify interrupt type/location and execute corresponding ISR[cite: 105]; 4. Check for other high-priority interrupts[cite: 105]; 5. Pop saved data from Stack and resume original process[cite: 105].

What is Polling and how does it differ from Interrupts?

Polling: The CPU repeatedly and actively checks a device or condition at regular intervals to see if it needs attention[cite: 107]. Difference: Interrupts are event-driven and CPU-efficient; polling wastes CPU time continuously checking idle devices[cite: 108].

Compare Interrupts vs. Polling on CPU usage, responsiveness, and complexity.

Interrupts: Efficient CPU usage, fast event responsiveness, but more complex to implement[cite: 108]. Polling: Inefficient CPU usage (wastes cycles), potentially delayed responsiveness, but simple to implement[cite: 108].

How does Multitasking achieve CPU Time Sharing?

The OS rapidly switches between multiple independent processes (each with its own memory space), giving the illusion of simultaneous execution[cite: 109].

What is Context Switching and how does it work?

The OS saves the current state (CPU registers, program counter) of a running process into a Process Control Block (PCB) and restores the saved state of the next scheduled process[cite: 110]. Managed by the OS Scheduler[cite: 110].

What are the 3 main duties of Resource Allocation in an OS?

1. Managed Distribution (allocates CPU time, memory, and I/O devices as needed); 2. Conflict Prevention (controls access to shared resources so processes don't interfere); 3. Dynamic Reassignment (tracks and reallocates resources as processes start, run, and terminate).

What are the 3 key aspects of OS Memory Management?

1. Allocation & Deallocation (assigning RAM and reclaiming it when unneeded); 2. Protection & Isolation (ensuring processes access only their own memory); 3. Efficient Use (minimizing waste via paging/segmentation)[cite: 111].

What is Resource Contention and its 3 major forms?

Resource Contention occurs when multiple processes compete for limited resources (CPU, memory, I/O)[cite: 112]. Forms: Deadlock, Livelock, and Thrashing[cite: 112].

What are Deadlock, Livelock, and Thrashing?

Deadlock: Processes wait indefinitely for resources held by each other[cite: 112, 115]. Livelock: Processes continuously change state in response to each other without making progress[cite: 112, 115]. Thrashing: System spends more time swapping pages than executing tasks due to overcommitted memory[cite: 112, 115].

Compare the solutions for Deadlock, Livelock, and Thrashing.

Deadlock: Kill or roll back processes to release resources[cite: 115]. Livelock: Pause, reorder, or introduce delays in process actions[cite: 115]. Thrashing: Reduce system load or increase physical RAM[cite: 115].

What is a Semaphore and how does it function?

A synchronization tool/variable used in multitasking to control access to shared resources[cite: 113]. Functions as a counter-based lock and a signaling mechanism between tasks[cite: 113].

What is a Control System?

A device or set of devices that manages, commands, directs, or regulates the behavior of other devices/systems using inputs to generate outputs[cite: 116].

What are the 3 main hardware components of a Control System?

1. Microprocessor (processes input signals); 2. Sensors (detect physical inputs); 3. Actuators (perform physical outputs)[cite: 117].

What is a Microprocessor in a control system?

An integrated circuit (chip) containing CPU functions (arithmetic, logical, control) that processes electrical input signals and generates output signals[cite: 118].

What is a Transducer and a Sensor?

Transducer: Any device that converts one form of energy into another (includes sensors and actuators)[cite: 119]. Sensor: A device that detects or measures a physical property and responds with a signal.

List 5 common types of Sensors and their applications.

1. Heat (measures temp, e.g., central heating, fire alarm)[cite: 107]; 2. Humidity (measures water vapour, e.g., greenhouses)[cite: 107]; 3. Infrared (measures radiation, e.g., security alarms)[cite: 107]; 4. Light / Photodiode (brightness, e.g., security lights)[cite: 107]; 5. pH (acidity levels, e.g., environmental monitoring)[cite: 107].

List 5 more types of Sensors and their applications.

1. Pressure / Piezoresistive (force applied, e.g., automatic doors)[cite: 107]; 2. Smoke (particles in air, e.g., fire alarm)[cite: 107]; 3. Sound (sound pressure, e.g., noise monitoring, voice control)[cite: 107]; 4. Tilt (angle of tilt, e.g., aircrafts, window alarms)[cite: 107]; 5. Touch (contact, e.g., robots)[cite: 107].

What is an Actuator and what does it require to operate?

A transducer that converts input energy (usually an electrical signal in IBCS) into physical motion[cite: 108]. Requires a control device (emitting a control signal) and an energy source[cite: 108].

List 6 common types of Actuators and their functions.

1. LED/Light bulb (creates light, displays info)[cite: 109]; 2. Heater (increases temp)[cite: 109]; 3. Cooling unit (decreases temp, e.g., AC)[cite: 109]; 4. Motor (spins objects, e.g., robots, elevators)[cite: 109]; 5. Pump (pushes air/water through pipes)[cite: 109]; 6. Buzzer/Bell/Siren (creates loud noises)[cite: 109].

What is an Analog-to-Digital Converter (ADC) and why is it needed in control systems?

Converts continuous analog data from sensors into digital binary data that can be processed by computers/microprocessors[cite: 110].

Explain the Input-Process-Output (IPO) model in Control Systems.

1. Input: Sensors capture analog input and ADC converts it to digital data[cite: 111]; 2. Process: Microprocessor processes digital data and computes output commands[cite: 111]; 3. Output: Transducers/Actuators turn digital data into physical motion or action[cite: 111].

What is Feedback in a Control System?

When either the system's output (or a derivative of the output) is sampled and fed back into the system as part of the input to alter subsequent operations[cite: 112].

What is an Open-Loop Control System?

A control system that does not use feedback to adjust its operation; it repeats the same pre-set action strictly based on input (e.g., TV remote, light bulb, coffee machine, toaster)[cite: 113].

What is a Closed-Loop Control System?

A system that uses a feedback loop to monitor output, calculate errors against a setpoint, and alter subsequent inputs to correct output errors (e.g., home thermostat, airplane autopilot)[cite: 114, 116].

What are the 3 key duties of a Control Algorithm?

1. Compares desired setpoint vs. actual measured output to calculate error[cite: 115]; 2. Decides corrective action based on error (e.g., adjust motor speed, voltage, valve)[cite: 115]; 3. Continuously updates in real time to keep system stable and close to setpoint[cite: 115].

How does a Home Thermostat function as a real-world control system?

Monitors room temperature via sensors and turns heating or cooling on/off to maintain a target set temperature[cite: 117].

How does Cruise Control in a car operate as a control system?

Automatically adjusts car speed by increasing or decreasing engine power to maintain a constant target speed[cite: 117].

How does an Automatic Washing Machine function as a control system?

Controls water levels, temperature, and spin cycles based on user settings, dynamically adjusting actions as the wash cycle progresses[cite: 117].