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Questions and Answers
What defines a preemptible resource?
Which scheduling method allows a process to resume execution only when it voluntarily blocks or terminates?
What is the primary goal of CPU utilization as a scheduling criterion?
What issue arises when processes wait indefinitely for resources held by each other?
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Which level of scheduling is primarily concerned with determining which processes will execute in the near future?
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Which component of a computer system is primarily responsible for controlling and coordinating hardware usage?
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What is the main function of the kernel in an operating system?
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What starts the operating system by loading the kernel into memory?
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Which of the following describes a feature of a multi-user operating system?
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Which of these components is NOT a function of the operating system?
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What role does the BIOS play during the startup of a computer?
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Which interface allows users to interact with the operating system through typed commands?
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Which of the following is a responsibility of the operating system regarding hardware?
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Which scheduling algorithm allows the process that has been waiting the longest to execute next?
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What is the primary function of memory management in an operating system?
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Which operating system architecture consists of a single executable file for the entire OS?
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What type of system call is responsible for creating a new process?
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What file system structure categorizes files into a tree-like format?
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In the context of virtual machines, what does the OS kernel and hardware representation collectively refer to?
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What does multiprogramming primarily aim to achieve?
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Which of the following is NOT a responsibility of process management in an operating system?
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What is the primary role of an operating system in relation to application software?
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Which of the following is not considered a goal of a system design?
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Which operating system type allows many users to connect to one computer while performing multiple tasks?
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What was a common way to load programs into memory in the early history of operating systems?
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Which aspect is NOT characteristic of real-time operating systems (RTOS)?
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What process allows multiple tasks to share resources within a computer system?
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Which of the following statements accurately describes load balancing in operating systems?
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In the context of operating systems, what does the term 'scaling' refer to?
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What is the primary difference between a program and a process?
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What does a Process Control Block (PCB) NOT contain?
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Which state best describes a process that is waiting for a resource to become available?
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What is the role of context switching in an operating system?
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Which of the following statements about processes is inaccurate?
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In which process state is a program actively executing on the CPU?
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What is the correct definition of a program?
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When does context switching typically occur?
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Study Notes
Components of a Computer System
- Hardware: Basic computing resources (CPU, memory, I/O devices).
- Operating System (OS): Controls and coordinates hardware usage.
- Application Programs: Software that uses system resources to solve user problems (e.g., word processors, games).
- Users: Individuals, machines, or other computers interacting with the system.
Small Components
- Process Management: Manages processes (programs in execution).
- Main Memory Management: Allocates memory to processes.
- File Management: Organizes and stores data on disks.
- I/O System Management: Manages input/output devices.
- Secondary Memory Management: Manages long-term storage.
- Networking: Enables communication between computers.
- Protection System: Enforces security measures.
- Command-Interpreter System: Provides a user interface.
Operating System
- A sophisticated program running on the CPU that acts as an interface between users and computer hardware.
- Hides hardware complexity from users.
- Manages the overall operation of the computer system including hardware, security, and interfaces for both system and applications.
Kernel
- In charge of the overall operation of the computer system.
- Remains in memory and controls overall system operations.
- Known as the "nucleus" of the OS.
Starting The OS
- Booting: Starting up a computer by loading the kernel.
- Bootstrap Program: Code in ROM (firmware) that loads the OS from storage.
- BIOS (Basic Input/Output System): Runs at startup to load the OS.
Functions of an Operating System
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Manages and Interacts with Computer Hardware:
- Controls CPU and RAM.
- Provides an interface for storage devices.
- Manages I/O devices
- Device Drivers: Software programs that allow hardware devices to be used by the OS and application software.
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Provides and Manages System Security:
- Implements user authentication, protects data and software.
- Single-user OS: Minimal security, the user has full authority.
- Multi-user OS: Login and password capability, protection of user's data stored on the server's central hard disk drives, protection and security for software programs.
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Provides System Interface:
- System Interface/Shell: The interface between the user and the computer.
- User interaction through Command Line Interface (CLI) (e.g., LINUX, DOS, UNIX) or Graphical User Interface (GUI).
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Provides Interfaces for Application Software:
- Designed for specific CPU types and allows software compatibility.
- Application software is developed for an operating system.
Operating System Objectives
- Convenience: Makes the computer more convenient to use.
- Efficiency: Allows computer system resources to be used efficiently.
- Ability to Evolve: Permits effective development, testing, and introduction of new system functions without interfering with service.
System Design Goals
- User goals: Convenient to use, easy to learn, reliable, safe, and fast.
- System goals: Easy to design, implement, and maintain, flexible, reliable, error-free, and efficient.
Types Of Operating Systems
- Single-User/Single Tasking OS: One user works at the OS and can perform one task at a time (e.g., MS-DOS).
- Single-User/Multi-Tasking OS: The most common form of OS used by PC and laptop, performing many tasks at once (e.g., Windows, macOS, Linux).
- Multi-User/Multi-Tasking OS: Many users connect to one computer and have unique sessions (e.g., UNIX, Linux).
- Real-Time Operating Systems (RTOS): Very fast, small OS that is built into a device and quickly responds to user input (e.g., Real-time Linux).
History of Operating Systems
- Began in the 1940s with hardware like ENIAC.
- Programs were loaded into memory manually using switches, punched cards, or paper tapes.
- Multiprogramming: Sharing of resources between more than one process.
- Time-sharing systems: Developed in the 1970s, multiple users have terminals (not computers) connected to the main computer and execute tasks on the main computer.
- Distributed Systems: Similar to networks as they no longer need to exchange information explicitly.
Today's Operating Systems
- Multiple processors
- Load balancing: Dynamically allocating tasks to the various processors.
- Scaling: Breaking tasks into several subtasks equal to the number of processors available.
- The Network (Internet): A single network-wide operating system.
Key services Provided By An OS
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Process Management:
- A program in execution, and the OS manages processes by allocating CPU time, memory, and I/O devices.
- Scheduling Algorithms:
- First-Come, First-Served (FCFS): Processes are executed in the order they arrive.
- Shortest Job First (SJF): The process with the shortest execution time is executed next.
- Round Robin (RR): Each process is assigned a time quantum, and the CPU is switched between processes after each time quantum.
- Memory Management: Ensures each process has access to the memory it needs to execute.
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File Management: Organizes and stores data on disks.
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File System Structures:
- Hierarchical: Example: UNIX file system (e.g., /home/user/Documents).
- Flat: Example: MS-DOS file system, where all files are in the same directory.
- Access Control: Restricts access based on user permissions.
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File System Structures:
Operating System Architectures
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Monolithic: The entire operating system is contained in a single executable file.
- Advantages: Simplicity, efficiency.
- Disadvantages: Difficult to debug, less secure.
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Microkernel: Moves as much from the kernel into user space, using message passing.
- Advantages: More modular, secure, less prone to errors.
- Disadvantages: Performance overhead.
- Hybrid: Combination of monolithic and microkernel architectures.
Virtual Machines
- Treat hardware and the OS kernel as a unified hardware interface.
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Types of Virtual Machines:
- System Virtual Machines: Emulate an entire computer system (e.g., VMware Workstation).
- Process Virtual Machines: Allow multiple processes to run on a single physical computer (e.g., Java Virtual Machine).
System Calls
- The interface between user-level programs and the kernel.
- Examples: open(), close(), read(), write(), fork(), exec().
- Types of System Calls:
- Process control: Create, terminate, load, execute, wait, etc.
- File Management: Create, delete, open, read, write, reposition, etc.
- Device Management: Request, release, and control I/O devices.
- Information Maintenance: Get or set system data, time and date, etc.
- Communication: Create and terminate communication links, messages, etc.
Process Management Responsibilities of The Operating System
- Process Creation and Deletion: The OS manages the lifecycle of processes from creation to termination.
- Process Suspension and Resumption: The OS can suspend processes (e.g., for resource management) and resume them as needed.
- Mechanisms for Synchronization and Communication: The OS provides tools for processes to synchronize actions and communicate with each other.
- Resource Allocation and Scheduling: The OS allocates CPU and memory resources to processes and schedules their execution.
Multiprogramming
- Definition: Multiprogramming (or multitasking) allows multiple processes to share CPU and other resources.
- Objective: To maximize CPU utilization by running multiple programs simultaneously.
Difference Between Program and Process
| Program | Process |
|---|---|
| A set of instructions designed to complete a specific task. | An instance of an executing program. |
| A passive entity residing in secondary memory. | An active entity created during execution, loaded into main memory. |
| Exists until it is deleted. | Has a limited lifespan and terminates after completion. |
| Static. | Dynamic. |
| Requires memory space for instructions only. | Requires CPU, memory, and I/O resources. |
| Has no control block. | Has a Process Control Block (PCB). |
| Consists of code and data. | Requires additional management information. |
| Does not change itself. | Multiple processes can execute a single program, with varying data. |
Process States
- Created/New: The initial state after creation, awaiting admission to the ready state.
- Ready: Loaded into memory, waiting for CPU allocation.
- Running: Actively executing on the CPU.
- Waiting: Awaiting resource availability or I/O operations.
- Terminated: Process has completed execution or has been killed.
Process Control Block (PCB)
- Definition: A data structure in the operating system kernel containing the information needed to manage a particular process. Called as "the manifestation of a process in an operating system."
- Location: Must be kept in an area of memory protected from normal user access or at the beginning of the kernel stack of the process.
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Attributes of PCB:
- Current state of the process.
- Process ID (PID).
- Pointers to parent and child processes.
- Process priority.
- Memory allocation pointers.
- Register save area.
- I/O information (devices allocated, opened files).
Context Switching
- Definition: The act of reassigning a CPU from one task to another. It occurs when the kernel transfers control of the CPU from an executing process to another that is ready to run.
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When Context Switching Occurs:
- When a process exits.
- When a process uses its time slice.
- When a process requires unavailable resources.
- When a higher priority process is ready to run.
Resource Allocation and Scheduling Concepts
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Resource Types:
- Pre-emptible Resources: Can take resources away and give them back later (e.g., CPU).
- Non-Preemptible Resources: Once given a resource, it cannot be reused until voluntarily given up (e.g., disk blocks.)
- Deadlock: Two or more processes wait indefinitely for resources held by each other.
- Starvation: One or more processes never gets a share of the resource.
Scheduling
- Definition: The method of determining which process runs next from the ready queue. It also refers to the way processes are assigned to run on the available CPUs.
- Scheduler: Module that moves jobs or processes from queue to queue.
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Types of Scheduling:
- Preemptive: Scheduler can interrupt a job and force a context switch.
- Non-Preemptive: Scheduler waits for the running job to explicitly (voluntarily) block/terminate.
CPU Scheduling Criteria
- CPU Utilization: Keep CPU busy.
- Throughput: Number of processes completed per time unit.
- Turnaround Time: Time from submission to completion.
- Waiting Time: Time spent waiting in the ready queue.
- Response Time: Time from submission until the first response.
- Fairness: Equal CPU time for all processes.
Levels of Scheduling
- Short-term Scheduling: Decides which of the ready processes will execute next (dispatcher).
- Medium-term Scheduling: Swaps processes in and out of memory.
- Long-term Scheduling: Determines which processes enter the ready queue.
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Description
This quiz covers the essential components of a computer system, including hardware, operating systems, and application programs. It also examines the small components integral to managing system resources and user interactions. Test your knowledge on how these elements work together to form a cohesive computing environment.
