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CPU Scheduler the scheduler selects a process from the processes in memory that are ready to execute and allocates the CPU to that process Dispatcher module that gives actual control of the CPU to the process selected by the scheduler. dispatch latency = time it takes for the dispatcher to stop one process an dstart another process. CPU- scheduling decisions may take place under the following 4 ..

Issue if one thread in a program calls fork(), does the new prcoess duplicate all threads, or is the new process single-threaded? solution some unix systems have chose to have 2 versions of fork(), one that duplicates all threads and another that duplicates only the thread that invoked the fork() system call. in muti thread process if one of thread invokes exec() system call, the program specifi..

Thread = basic unit of CPU utilization , Thread ID + PC(program counter) + register set + stack in multi thread = code ,date ,file are shared but they have their own register and stack. benefits Responsiveness = muti thread operate simultaneously even if one thread takes long time or get blocked , user can still interact with other theads that is working fine. Resource sharing = allows an applic..

Sockets Socket = end point of communication link for each process == IP Address + Port number Servers implementing specific services listen to well known ports ( telnet=23 , ftp=21 , web,http=80) ports below 1024 is well known and reserved for specific services. Remote Procedure Call(RPC) RPC is a protocol that one program can use to request a service from a program located in another computer. ..

IPC using shared memory requires communicating process to establish a region of shared memory. shared memory region reside in the address space of the process creating shared memory segment other process that wish to communciate using this shared-memory segment must attach it to their address space. normally the OS tries to prevent one process from accessing antoher process's memory but shared m..

A process may create several new processes, via a create-process system call , during the course of execution creating process = parent process created new process = children of that parent process children can create children process , forming a tree processes. a tree process on a typical Solaris system Parent child Execution 1. The parent continues to execute concurrently with its children. = ..

The state of process is defined by the current activity of process. new = the process is being created running = Instructions are being executed waiting = The process is waiting for some event to occur (I/O operation) ready = the process is waiting to be assigned to a processor terminated = the process has finished execution interrupt = some higher priority process came into schedule and interru..

virtual machine implementation can be software. at the base we are sharing same hardware resources. Virutal machine software (virtual machine implementation ) run in kernel mode virtual machine itself (vm1~3) runs in user mode. Inside virutual machine they have their own User mode and Kernel Mode but they run in a physical User mode(main) for each virutal machine there will be particular area in..

Sysetm programs are located between application program and OS. System programs categories File Management create , delete copy rename , print ,dump , List , and generally manipulate files and directories. Status information Date, Time , Amount of available memory or disk space , number of users , detailed performance , logging and debugging information File modification Several text editors may..

commonalities 1. multiprogramming without mutiprogramming single user will keep CPU and I/O devices busy all the times because once cpu takes users job it won't be able to take any other job until it finishes. with mutiprogramming CPU util will increase by organizing jobs so that CPU always has one to execute with mutiprogramming if job1 tries to use I/O devices CPU doesn't wait for job1 it exec..