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OS (Lecture 3, Lecture 1. Basic concepts and definitions of OS concepts.,…

- - - - The main advantage of a microkernel architecture is that it provides a more secure and stable operating system. Since only the most essential services run in kernel space, the attack surface of the operating system is reduced, making it more difficult for an attacker to exploit vulnerabilities. Additionally, if a user-level process crashes, it will not affect the stability of the entire system, since the microkernel is responsible only for managing processes and memory.
    - - Single Executable: The entire application is packaged and deployed as a single executable file. All components and modules are bundled together.
        
        Single Executable: The entire application is packaged and deployed as a single executable file. All components and modules are bundled together.
        
        Shared Memory: All components within the application share the same memory space. They can directly access and modify shared data structures.
        Monolithic Deployment: The entire application is deployed as a single unit. Updates or changes to the application require redeploying the entire monolith.
  - - - 2.Simplicity: The design of a monolithic kernel is simpler since all operating system services are provided by a single binary. This makes it easier to develop, test and maintain.
      - 3.Broad hardware support: Monolithic kernels have broad hardware support, which means that they can run on a wide range of hardware platforms.
        
        4.Low overhead: The monolithic kernel has low overhead, which means that it does not require a lot of system resources, making it ideal for resource-constrained devices.
        
        5.Easy access to hardware resources: Since all code runs in kernel space, it is easy to access hardware resources such as network interfaces, graphics cards, and sound cards.
        
        6.Fast system calls: Monolithic kernels provide fast system calls since there is no overhead of message passing between user-level processes
        
        7.Good for general-purpose operating systems: Monolithic kernels are good for general-purpose operating systems that require a high degree of performance and low overhead.
        
        8.Easy to develop drivers: Developing device drivers for monolithic kernels is easier since they are integrated into the kernel.
  - - - Thread: A thread is the smallest unit of processing in multitasking programs. Threads execute within a process and share a common process address space.
      - Concurrency: Concurrency refers to the simultaneous execution of more than one thread. This may involve running multiple tasks simultaneously on multiple processors.
      - Synchronization: Synchronization refers to methods and techniques that allow threads to interact and exchange data without conflicts or races.
      - High-priority processes are processes that interact with users and perform certain work for them
      - Background processes are processes that are not related to specific users, but perform a number of specific functions. Most of the time, such processes are spent in sleep mode, activating only as active activity appears (e-mail, web pages, printing information, etc.). Such background processes are often called daemons.
    - - In UNIX, there is only one system call to create a new process - fork. This call creates an exact copy of the parent process (parent and child have the same memory image, the same configuration description lines, and the same open files.).
    - - Generation - conditions are being prepared for the first execution on
        processors;
      - Active state or "execution" state - the program is running on
        processors;
        
        Termination – normal or emergency termination of execution
        program, after which the processor and other resources are not provided to it.
      - Waiting or blocking – the program is not running on the processor
        due to the employment of a certain necessary resource;
    - - Interprocess interaction
        (Inter-Process Communication, IPC)
        
        There are two types of processes:
        
        independent processes – execution of other processes does not affect processes
        
        cooperating processes - can be influenced by other executables
        processes.
      - Message transmission technologies
        
        A socket is an abstract connection endpoint through which a process
        can send or receive messages.
      - additional information for lecture 6
        
        https://www.youtube.com/watch?v=dJuYKfR8vec&authuser=0
        
        https://www.youtube.com/watch?v=LuuSXWkDJOo&authuser=0
        
        https://www.youtube.com/watch?v=fViAyFLOYxU&authuser=0
        
        https://www.youtube.com/watch?v=uHtzOFwgD74&authuser=0
        
        https://www.youtube.com/watch?v=uagKTbohimU&authuser=0
        
        https://www.youtube.com/watch?v=S3mS8MR7bUY&authuser=0
        
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      - Lecture 7
        
        Planning (scheduling) of processes and flows
        
        The main purpose of planning for a uniprocessor system is as follows
        organizing the execution of several threads on one processor, in which the user of the system would have the impression that they are executed simultaneously.
        
        From the point of view of scheduling, the execution of a thread can be represented as an interleaving cycle
        calculation periods (processor usage) and waiting periods
        input-output The time interval during which the thread executes only processor instructions, called the processor usage interval (CPU burst), the time interval when the thread waits for input output is an intervalinput-output (I/O burst).
        
        Flows that spend more time on calculations and less time on input-
        output, called limited capabilities of the processor (CPU bound). Threads that spend most of the time waiting for I/O,
        called I/O bound.
        
        Types of planning
        
        Long Term Scheduler
        
        Also knowns as Job Scheduler. It selects the process that are to be placed in ready
        queue. The long term scheduler basically decides the priority in which processes must
        be placed in main memory.Processes of long term scheduler are placed in the ready
        state because in this state the process is ready to execute waiting for calls of execution from CPU which takes time that’s why this is known as long term scheduler.
        
        Medium-Term Scheduler
        
        Also knowns as CPU Scheduler. It places the blocked and suspended processes in the secondary memory of a computer system. The task of moving from main memory to secondary memory is called swapping out. The task of moving back a swapped outprocess from secondary memory to main memory is known as swapping in. The
        swapping of processes is performed to ensure the best utilisation of main memory.
        
        Short-Term Scheduler
        
        It decides the priority in which processes is in the ready queue are allocated the
        central processing unit (CPU) time for their execution. The short term scheduler is also referred as central processing unit (CPU) scheduler.
        
        https://drive.google.com/file/d/1uy9yzicf5AjdgH7byj5-CzsPRCpPvw4c/view
        
        Lecture 8
        
        Organization of virtual memory
        
        1)Memory: An important resource that needs to be managed.
        2)Memory Capacity: The amount of available memory that becomes important when considering the size of computer programs.
        3)Parkinson's Law: The principle that states that the size of programs grows faster than the amount of memory.
        4)Operating systems: Systems that create abstractions from memory and manage them.
        
        6)Memory Hierarchy: A concept that defines the different levels and types of memory in a computer.
        
        5)Cache memory: Megabytes of fast, expensive and volatile memory.
        
        7)Disk drives: Terabytes of slow, cheap storage such as HDDs.
        
        Memory without using abstractions
        
        Memory Abstraction: The concept of creating a model that hides the physical details of memory to simplify programmer interaction.
        
        Universal Machines: Computers that existed until 1960 and did not use memory abstractions.
        
        Mini-Computers: Computers until 1970 that also did not use memory abstractions.
        
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        Three simple ways to organize memory in the presence of an operating system and
        one process user (there are also other options)
        
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        Lecture 9
        
        Page Replacement Algorithms: Special strategies that determine which page to remove from the main memory when a page fault occurs.
        
        Optimal Page Replacement Algorithm: A hypothetical algorithm that selects the page for removal that will not be used for the longest period.
        
        Not Recently Used Algorithm (NRU): An algorithm that categorizes pages based on the R (referenced) and M (modified) bits, and removes the page with the lowest category when a page fault occurs.
        
        First-In-First-Out Algorithm (FIFO): A page replacement strategy where the page that was first loaded into memory is removed when a page fault occurs.
        
        Second-Chance Algorithm: A modification of the FIFO algorithm that checks the R bit of the oldest page, removes the page if the R bit is 0, and moves the page to the end of the list if the R bit is 1.
        
        Clock Algorithm: An efficient page replacement algorithm that uses a cyclic list of pages, and when a page fault occurs, selects the page pointed to by the "clock hand," considering the R bit.
        
        Lecture 10
        
        key concepts and terms:
        
        Hard Links: Hard links in file systems that allow multiple names to refer to the same data on disk.
        
        Symbolic Links Special files that contain the name of a file or directory to which they point.
        
        File Attributes : Characteristics of files, such as the file name, file type, size, security attributes, and time attributes.
        
        Approaches to File Usage by Processes : Stateful and stateless approaches to using files in processes.
        
        File Operations : Fundamental operations such as opening, closing, creating, deleting, reading, writing, moving the current position pointer, and getting or setting file attributes.
        
        POSIX File Operations : Set of system calls for file operations in UNIX-compatible systems, including open(), close(), read(), write(), lseek(), stat().
        
        Win32 API File Operations ( Win32 API): Functions for file operations in the Win32 environment, such as CreateFile(), CloseHandle(), ReadFile(), WriteFile(), SetFilePointer(), GetFileAttributesEx().
        
        Directory Operations : Basic operations like creating, deleting, opening, closing, reading an element, and moving to the beginning of a directory.
        
        Lecture 11
        
        10 key concepts and terms from lecture 11
        
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        Lecture 12
        
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- - - - 2.Loading programs into RAM and executing them.
        
        3.Providing standardized access to peripheral devices (input and output devices).
        
        4.Managing RAM (allocation among processes, organizing virtual memory).
        
        5.Managing access to data on non-volatile storage devices (such as hard drives, optical disks, etc.) organized in various file systems.
        
        6.Providing a user interface.
        
        7.Recording system error information.
    - - 1.Parallel or pseudo-parallel execution of tasks (multitasking).
        
        2.Efficient allocation of computing system resources among processes.
        
        3.Resource access separation for different processes.
        
        4.Ensuring reliable computations (preventing one computational process from intentionally or mistakenly affecting computations in another process) based on resource access separation.
        
        5.Interprocess interaction: data exchange and mutual synchronization.
        
        6.Protection of the system itself, as well as user and program data, from user actions (malicious or due to lack of knowledge) or applications.
        
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