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OS (Modes Of Operations image, IO Devices, Syncronization Solves the…

- - - - איתם ניתן לגשת לOS.
        סוגים של System Calls:
        
        שליטה בתהליכי CPU
        
        ניהול קבצים או מכשירים
        
        תחזוק מידע ודאטא
        
        תקשורת
        
        הגנה
      - Process
        
        Context Switch
        לא בהכרח ששימוש בשיטה זו מהירה יותר, אלא רק במקרה וחוסכים המתנה בחלק מהתוכניות
        
        When would we use Context Switch
        
        Process Creation = fork
        Each process own an Process ID (pid)
        
        Inter-Procces Communication
        The way processes communicate with each other
        
        Signal
        
        Pipe
        send data from one process to another
        
        Unnamed pipe
        pipes that arent related
        
        named pipe
        related piped
        
        mknod
        create a FIFO(pipe)
        
        Memory Mapped File
        A file both process can read from, as the way they're communicating
        
        Exec()
        Give an order to a child of a parent, which is different from the parent's code
        (instead of cloning, use the child for other thing)
        
        Diagram Process State
        
        Memory Protection
        Each process own a BASE and LIMIT, which indicates the beginning and the end of process orders
        When process points line X it means he actually reads line BASE + X. means he reads all the code starts from base.
        this way the data is not leaking.
        
        Processees Types
        
        Process Control Block (PCB)
        The OS saves kind of a Data structure for each process with contains:
        
        Process Memory Segment
        What the memory of each process contain
      - Threads
        single unique path of execution
        Each thread has irs own program counter, stack and registers
        but all threads share its memory (code + data- heap and static space, NO stack space)
        
        Process vs Thread
        Every process has a least one thread
        
        Shared vs Private
        
        Disadvantages
        
        The kernel is not familiar with the process' threads. if one thread uses I/O, the entire process is waiting.
        
        System Calls required, which is an overhead
        
        User level vs Kernel Threads