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Questions and Answers
What characterizes a real-time operating system?
What characterizes a real-time operating system?
In which type of multiprocessor system do each of the processors have their own memory module?
In which type of multiprocessor system do each of the processors have their own memory module?
What is a significant characteristic of time-sharing operating systems?
What is a significant characteristic of time-sharing operating systems?
What is not a feature of real-time operating systems?
What is not a feature of real-time operating systems?
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Which operating system requires high-speed interaction between tasks?
Which operating system requires high-speed interaction between tasks?
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In a loosely coupled multiprocessor system, what is the advantage regarding memory conflicts?
In a loosely coupled multiprocessor system, what is the advantage regarding memory conflicts?
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Which statement about tightly coupled multiprocessor systems is true?
Which statement about tightly coupled multiprocessor systems is true?
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Which statement correctly reflects a difference between time-sharing and real-time operating systems?
Which statement correctly reflects a difference between time-sharing and real-time operating systems?
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What is the primary function of an operating system in managing multiple applications?
What is the primary function of an operating system in managing multiple applications?
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Which of the following states indicates that a process has completed its execution?
Which of the following states indicates that a process has completed its execution?
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Which scheduling algorithm is characterized by serving processes in the order they arrive?
Which scheduling algorithm is characterized by serving processes in the order they arrive?
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What is the role of the operating system in transitioning process states?
What is the role of the operating system in transitioning process states?
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In the context of process scheduling, what does the 'Waiting' state signify?
In the context of process scheduling, what does the 'Waiting' state signify?
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Why does the operating system try to limit frequent transitions between CPU cores?
Why does the operating system try to limit frequent transitions between CPU cores?
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Which process state indicates that the process is ready but has not yet been assigned to a processor?
Which process state indicates that the process is ready but has not yet been assigned to a processor?
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What is a primary concern when multiple programs attempt to run in parallel on the same system?
What is a primary concern when multiple programs attempt to run in parallel on the same system?
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What is the primary purpose of the Ready Queue in a process scheduling system?
What is the primary purpose of the Ready Queue in a process scheduling system?
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In what situation does a process move to the Waiting Queue?
In what situation does a process move to the Waiting Queue?
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Which of the following metrics is typically NOT used by an OS to determine scheduling priorities?
Which of the following metrics is typically NOT used by an OS to determine scheduling priorities?
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What does the Job Queue maintain?
What does the Job Queue maintain?
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Which scheduling algorithm prioritizes processes based on the length of their next CPU burst?
Which scheduling algorithm prioritizes processes based on the length of their next CPU burst?
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Why do operating systems seek to ensure fairness and liveness in scheduling?
Why do operating systems seek to ensure fairness and liveness in scheduling?
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What is the primary impact of CPU Utilization in scheduling criteria?
What is the primary impact of CPU Utilization in scheduling criteria?
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What happens when a time slice expires for a process in Round-Robin scheduling?
What happens when a time slice expires for a process in Round-Robin scheduling?
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Study Notes
SWE Tracks' Renovation
- The renovation of SWE Tracks is in view of SWEBOK V3.0.
Operating Systems Lecture 1
- The course duration is 6 hours.
- Two lectures (6 hours)
- Evaluation: A comprehensive exam after all conceptual courses.
- Course outlines include: Introduction to Operating System and Computer System, Processes and Scheduling, Memory Management, I/O Management, File Systems, Access and Protection, Virtualization and User Interface and Shells
Course Presenter
- Ahmed M. Abdelfattah, Project Manager
- ITP (Intensive Training Program)
- ITI (Information Technology Institute)
Computer System Components
- Hardware: Provides basic computing resources (CPU, memory, I/O devices).
- Operating System: Controls and coordinates hardware use among various application programs.
- Applications: Define ways system resources are used to solve computing tasks (compilers, database systems, video games, business programs).
- Users: People, machines, and other computers.
Operating System Definition
- A program that controls the execution of application programs.
- An interface between the user and hardware.
- Masks hardware details from applications, the OS handles the hardware details.
Examples of Operating Systems
- Linux-based OS
- Microsoft Windows
- macOS (Apple's computers and client models)
- iOS (Apple's smartphones/tablets)
- Android
Operating System Definition
- The general definition of any system: Some components integrated together to perform a desired task.
- The definition of a computer operating system: Some components integrated together for operating the computer system (hardware and software).
- An operating system (OS), commonly referred to as OS, is a program that controls the execution of other programs running on the system. It acts as a facilitator and intermediate layer between different software components and the computer hardware.
- When any operating system is built, it focuses on three main objectives: Efficiency of the OS in terms of responsiveness, fluidity, etc., Ease of usability to the user in terms of making it convenient, Ability to abstract and extend to new devices and software.
Programming Language for OS
- The UNIX operating system's development started in 1969 and was rewritten in C in 1972.
- Windows 1.0 was released in 1985, mostly written in C with some assembly.
- Linux kernel development started in 1991 and is also written in C.
- Most operating systems are written in C/C++.
Computer Operating System
- When a computer turns on, the processor executes instructions. The first code that runs is for boot flow, called bootstrap. This is a framework stored in ROM containing basic input/output instructions (BIOS).
- All these instructions need to be abstracted and handled efficiently. The operating system facilitates this.
Role of the Bootstrap
- Bootstrapping is the process of loading a set of instructions when a computer is first turned on or booted.
- The bootloader or bootstrap program then loads and initializes the OS.
Typical OS Loaders
- NT Loader (NTLDR): A bootloader for Microsoft's Windows NT OS, usually runs from the hard drive.
- Linux Loader (LILO): A bootloader for Linux, generally runs from a hard drive or floppy disk.
- GNU Grand Unified Bootloader (GRUB): A multiboot specification that lets users choose between several OSs.
Bootstrap Procedure
- The Bootstrap program runs.
- The Operating System is loaded.
- The Operating System runs.
Bootstrapping (Cont.)
- Prior to bootstrapping, a computer starts with a blank main memory.
- The bootstrap allows the sequence of programs to load in order to initiate the OS.
- The OS is the main program that manages all programs and performs tasks.
Services Provided by the OS
- Facilities for Program Creation (editors, compilers, linkers, debuggers)
- Program Execution (loading in memory, I/O and file initialization)
- Access to I/O and files (specifics of I/O and file formats)
- System Access (protection in access to resources and data)
- Resolves conflicts for resource contention
Example Using C Programming Language
- In early versions of C under DOS, the code *ptr = 5; may cause a program crash.
Security and OS
- Qubes OS (Linux based) is considered a secure operating system. It isolates user applications into distinct entities, like a virtual machine. It's easy for users with Linux experience but not for beginners.
OS Categories – Usage Types
- Batch: Groups jobs that perform similar functions and are processed in batches.
- Time Sharing: Systems where multiple users/applications access common hardware.
- Parallel: Distributed systems with a single operating system to coordinate hardware access.
- Network– Distributed: Systems connected via a network protocol.
- Real-Time: Systems needing fine-grained time precision in execution and responsiveness.
Comparison Between Time-Sharing and Real-Time
- Time Sharing: Switching method/function available. Any program modification can be possible. Computer resources are shared.
- Real Time: Switching method/function unavailable. Modifications are not available. Computer resources are not shared.
Loosely and Tightly Coupled Multiprocessor System
- Loosely Coupled: Each processor has its own memory module. Efficient when tasks run on different processors, minimal interaction. Low memory conflict. Less expensive.
- Tightly Coupled: Processors share memory modules. More efficient for high-speed or real-time processing. High memory conflict. More expensive.
OS in Embedded System Domain
- Linux and Android are powerful operating systems used in embedded systems today.
- Selection depends on usage: Wireless connectivity, graphics, etc.
- Linux can perform functions of Android, however, Linux is complex and more challenging for beginners but provides better results once understood.
Device Controller and Driver
- Device driver: A piece of code inside the operating system that's designed to communicate with the hardware.
- Device controller: An electronic component consisting of chips which is connected between the device and operating system
Importance of Knowing the OS
- Software developers need to understand the running environment (OS) to function correctly.
- Understanding OS interfaces and functionality affects software development.
- The choice of programming languages, runtime features, and IPC protocols are OS-dependent.
- Debugging applications, particularly issues involving performance.
Operating System Responsibilities
- Abstracting hardware complexities, Supporting multiple users, Executing multiple applications concurrently
- Scheduling CPU time, Managing memory, I/O and resource management, File systems, Handling user interactions.
Operating System Components
- System Calls, File System, I/O Manager, Scheduler, Memory Manager, Drivers, Kernel/OS modules/Microservices
OS Definition
- Most OSs have a core part (kernel) handling complex, low-level functions. It resides in memory.
- OSs also have libraries, applications, tools (e.g., browsers, frameworks).
Kernel
- The core of all operating systems.
- Provides a basic interface between the computer and the rest of the OS.
- Responsible for managing the central processor.
- Functions include switching between programs, hardware device control, memory management, process management, scheduling, and inter-process communication.
Utility Programs
- System software for effective management.
- Examples: File Manager, Task Manager, Uninstaller, File Compressor, Disk Scanner.
File Manager Example
- Used to manage and view files in a computer system.
- Provides file viewers (like Windows Explorer).
- Functions include displaying file lists, organizing files in folders, copying/renaming/deleting/moving files, and creating shortcuts.
Processes and Scheduling: Content
- Introduction to Scheduling
- Process Concept
- Process Contents
- Process States
- Process Control Block (PCB)
- Context Switching
- Scheduling
Program and Process Concepts
- A program is a set of capabilities provided through processed code, built for a specific operating system.
- When activated, the operating system assigns a process ID and other metrics for tracking.
- At a high level, an executing program is known as a process in the operating system. (Jobs and processes are sometimes used interchangeably.)
Introduction to Scheduling
- One of the OS' primary functions is to run multiple concurrent applications efficiently while managing their access to system resources.
- When multiple programs run concurrently, conflicts may arise when competing for resources like the CPU, memory, and other devices.
- The operating system's scheduling function orchestrates the execution and subsequent requests to avoid these conflicts.
Scheduling Algorithms (Examples): FCFS, RR, SJF, SJF (preemptive), Priority (non-preemptive), Priority (preemptive)
- Various algorithms exist to handle processes efficiently.
- Detailed examples with specific process details provided.
Context Switching
- OS swaps the currently executing process with another, to allow different applications to run, with the help of context switching.
- When the operating system needs to switch processes, it saves the currently running processes context, switches to the new process and then defines a new context for processing. This method ensures accurate execution from where the application was interrupted.
Process Control Block (PCB)
- Unique identifier for a program or process.
- Current state of a process is identified
- Hierarchical structure for processes (e.g., parent-child process).
- Priority level of a process (e.g. high,medium,low,critical, real-time etc.) to be used for scheduling.
- Details of CPU registers to manage the running process on a specific CPU core.
Execution of the system call
- Processes typically execute in user mode.
- A system call interrupts the user-mode execution and switches to kernel mode.
- The system call is executed. Control then returns to user mode.
User Mode vs Kernel Mode
- User mode: The operating system is running an application like a simple text editor.
- Kernel mode: The OS handles requests or when a system call is made
System Calls
- System calls are how a process interacts with the operating system.
- They are instructions available in assembly language.
API - System Call (Example)
- The printf() in C makes a system call.
- A software function converts data to byte sequences.
- Those byte sequences are passed to the write() system call.
System Calls Types
- Divided into types based on their function: Process control, File management, Device management, Information maintenance, Communications, and IPC. Specific functions (e.g., load,execute, create file etc. ) under these categories are listed.
Examples of Windows and Unix System Calls
- Detailed list of system calls used in Windows and Unix/Linux operating systems.
- Each system call is precisely identified.
Difference Between 32-bit and 64-bit Operating Systems
- 32-bit processors can address 4GB of RAM.
- 64-bit processors can address significantly more RAM (18 quintillion bytes or 18 exabytes).
- 64-bit processors can run 32-bit or 64-bit OSs; however, using a 32-bit OS on a 64-bit processor will restrict its capabilities.
Thread Concepts
- Threads are considered as lightweight processes and they aid in achieving parallelism.
- Each thread pertains to a specific process.
- Examples of thread usage in programming include: chat programs and games where actions are done concurrently.
Comparison Between Process and Thread
- Processes are resource-intensive.
- Thread switching involves less overhead.
- Threads can share resources.
- One thread can execute while another is blocked.
Benefits of Threads
- Threads can effectively use multiple processors.
- Faster context switching.
- Enhanced throughput, which means more jobs in a specific time frame.
- Thread communication is simplified.
- Shared resources are easily accessible
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