CSU CS370 Midterm Chapter 1

List instructions that might be usable only from supervisor mode in a dual-mode processor

-Handling Interrupts -To switch from user mode to kernel mode -Input-Output management -To switch from user to kernel mode, mode bit should be 0

What resources must be protected by the operating system?

-I/O -Memory -CPU -System files

Define operating systems in terms of what they do.

-Referee: Manage sharing of resources Protection, and isolation. -Illusionist: Provide clean, easy to use abstractions of physical resources -Glue: Common services -Storage, Window System, Networking -Sharing, Authorization -Look and feel

What is time-sharing? What are the main advantages of time-sharing?

-Timesharing is a logical extension in which CPU switches jobs so frequently that users can interact with each job while its running, creating interactive computing -*Response time* should be <1 second -Each user has at least one program executing in memory -> process -If several jobs ready to run at the same time -> CPU Scheduling -If processes dont fit in memory, *swapping* moves them in and out to run -*Virtual memory* allows execution of processes not completely in memory.

How is time-sharing usually implemented?

-Using CPU scheduling and multiprogramming to provide each user with a small portion of a time-shared computer. -CPU time is divided among all the users on a scheduled basis -The OS allocates a set of time to each user. When this time is expired, it passes control to the next user on the system -The time allowed is extremely small so it seems that all the users have their own CPU.

What is multiprogramming?

-run multiple programs at seemingly at the "same time" -Needed for efficiency -Single user cannot keep CPU and I/O devices busy at all times -Organizes jobs (code and data) so CPU always has one to execute -A subset if total jobs in system is kept in memory -One job is selected and run via job scheduling -When it has to wait (Ex. I/O), OS switches to another job

What is the difference between I/O-bound jobs and CPU-bound jobs?

CPU Bound: means the rate at which process progresses is limited by the speed of the CPU. A task that performs calculations on a small set of numbers, for example multiplying small matrices, is likely to be CPU bound. -Speed would increase if the CPU were faster I/O Bound: means the rate at which a process progresses is limited by the speed of the I/O subsystem. A task that processes data from disk, for example, counting the number of lines in a file is likely to be I/O bound. -Speed would increase if the I/O subsystem were faster

What is an interrupt vector?

Dispatches interrupt to correct handler -Context switch at start and end -Based on priority -Some nonmaskable -Interrupt chaining if more than one device at same interrupt number

What is a dual mode operation? How does the system switch between jobs?

Dual-Mode operation allows OS to protect itself and other system components -User mode and kernel mode(supervisor) Switch between jobs -change the mode bit -User mode bit = 1 -Kernel mode bit = 0 User process executing(user) -> Calls system call(user) -> execute system call(kernel) ->