Stevens Institute Of Technology CS 492 _ Complete Midterm Review.

CS492 Complete Midterm Review Processes: ● Process - a program in execution ● A single CPU at any given time may only run one process ● CPU Utilization: 1 - p​n ● Processes don’t shar e memory address space Syscalls: Calling a kernel mode service from user mod program ● switches execution to kernel mode ● Programming interface to services provided by the OS ● Typically written in a high-level language ● APIs: ○ Win32 API (Windows) ○ POSIX API (POSIX-based systems: UNIX, Linux, MacOS) ● Types of syscalls: ○ Process control ○ File management ○ Device management ○ Information maintenance ○ Communications ● Return codes ○ s is -1 if error has occurred ○ fd is a file descriptor ○ n is a byte count ○ position is an offset within the file ● OS-to-Process Communication: a way for the OS to inform the process about something ○ “Asks” process to take an action based on the information Threads: ● Inter-Process Communications: Two main functions of an OS: ● Resource management ● User-friendliness for interaction with the hardware Scheduling: ● Scheduling decisions may take place when a process/thread ○ Is created ○ In running state exits ○ Blocks on IO, or an event ● Scheduling decisions may take place when an interrupt occurs○ Clock interrupt ■ Switch from running to ready ○ IO interrupt, or (unblocking) syscall ■ Switch from blocked to ready ● Scheduling takes place at clock interrupts ● A way for a system to keep track of time ○ Interrupt at periodic intervals ○ Implemented using a hardware clock interrupt ○ High priority ● Non-preemptive scheduling ○ Voluntary process switch(yield) ○ Process switch on blocking calls ○ The scheduler gets involved only at exit or on request ● Preemptive scheduling ○ Involuntary process switch ○ For every clock interrupt, running process may be suspended and switched with another process(if there is any) ● Different environments different scheduling algorithms are needed ● Different application areas have different goals ● Environments ○ Batch Systems ○ Interactive Systems ○ Real-time Systems ● Scheduling Algorithms Goals ○ All Systems ■ Fairness: giving each process a fair share of the CPU ■ Policy enforcement: seeing that stated policy is carried out ■ Balance: keeping all parts of the system busy ○ Batch Systems ■ Throughput: maximize jobs per hour ■ Turnaround time: minimize time between submission and termination