Operating System Support and CPU Scheduling

what is medium-term scheduling?

Involves swapping out a process from the main memory. The process can be swapped in later from the point it stopped executing.

Why was the monitor important in a batch system?

It acts as the operating system, where it receives instructions.

what is a CPU scheduler?

It selects a process among the processes that are ready to execute and then allocates it into the CPU.

What is shortest job first algorithm?

It uses priority scheduling where it prioritizes the executing processes based on the shortest burst time. Possibility of starvation With preemptive scheduling method the scheduler can interrupt running process with another that has shorter process time. With non-preemptive scheduling method a process cant being interrupted even if another has a shorter burst time.

what is the round-robin algorithm?

It's a preemptive scheduling method designed for a time sharing system. Uses a small-time unit called a time quantum that's 10-100 milliseconds. If the quantum is to big then the scheduling is same as FCFS, if to small then increases overhead. When an interrupt occurs, the current running process is placed in the Ready Queue. Next ready job is selected

what is the first come first serve scheduling algorithm?

Its a non-preemptive scheduling method that uses first-in-first out queue for implementation that results in long waiting time.

what is a batch system?

Jobs are bundled together via a job card with instructions which allows them to be processed without intervention.

describe the process creation?

(1) Assign a unique process identifier (2) Allocate space for the process (3) Initialize PCB (4) Create appropriate linkages (5) Create expanding other data structures

What are five areas that operating systems will continue to develop in the future?

(1) Processes (2) Scheduling and resource management (3) Memory management (4) Computer system structure (5) Information protection

CPU scheduling decisions may take place when a process:

(1) Switches: "running <--> waiting" state (2) Switches: "running <--> ready" state (3) Switches: "waiting <--> ready" state (4) "Terminate"

what is a computer system?

A collection of hardware and software resources

what is a process control block?

A data structure in the kernel that contains information to manage a process.

what is the five state model?

A process can be in one of five states along with there being a queue that holds processes that are not running in the OS.

what is a block queue?

A queue that holds a process from executing until some event occurs

what is a process?

A unit of activity of a running instance of a program that's being executed by CPU.

what are some of the services that an operating system provides?

Accounting/monitoring of performance controlled access to files error detection and response Schedule/control processes to run applications.

what is a non-preemptive scheduling method?

Allows a process to have full CPU time until it terminates or is pushed to the waiting state. CPU utilization is low but less starvation, and no overhead. Running process becomes suspended as a result of its own action

what is the multiprogramming principle of a batch system?

Allows the CPU to have multiple jobs processing which maximizes CPU time. Makes the CPU "switch" to another job, when one job needs to wait for I/O processing.

what is waiting time?

Amount of time a process has been waiting in the ready queue. Waiting time = (actual starting time) - (arrival time)

Whats are some of the system objectives for scheduling in regards to processes being executed by the processors?

CPU Utilization Throughput Turnaround time waiting time Response time

what is preemptive scheduling?

CPU time is allocated according to clock cycles for a limited time so processes get the CPU for a short time. Running processes can be interrupted for a higher priority process. High CPU utilization and a process cant monopolize the CPU but has high overhead.

how does the kernel work in regards with the CPU, main memory, and I/O devices?

CPU: Kernal decides which running program is allocated to CPU Main memory: Kernel decides which memory each process can use and what to do when there isn't enough memory. I/O devices: Kernel allocates request from applications to perform I/O operations for the correct device.

What are the three components of a process?

Context, which is the execution context of the program for the OS. Data: Which is the data that's needed by the program Program: an executable program

what is an operating system?

Controls and coordinates the use of the hardware among applications and users. Manages software resources and provides common services.

what are the objectives of a operating system?

Efficiency: use system resources in a efficient manner and exploit hardware resources. Convenience: provide services to users and be convenient to use. Ability to evolve: allow for development, testing, and introduction of new system functions

What are the different scheduling algorithms?

First-Come First-Served Algorithms Priority Scheduling Algorithms Round-Robin (RR) Algorithms Shortest Job First Algorithms

what are the different generations of operating systems?

Generation one: plug boards and serial processing. Generation two: batch systems. generation three: multi-programming batch systems Generation four: real-time, multiprocessor, distributed systems.

what is a dispatcher module?

Gives control of the CPU to the process selected by the short-term scheduler and involves jumping to the proper location in the user program to restart that program.

what are the four components that computer systems are divided into?

Hardware, operating systems, application programs and users

what is throughput?

How many jobs the CPU has completed in the total time Throughput = (numbers of job/total time)×100

how is single programming batch system different then a multiprogramming batch system?

In single batch processing, CPU must wait for I/O instruction to complete before preceding. Computer spends 96% of time waiting for I/O device

what are the types of CPU scheduling?

Long term scheduling Midterm scheduling Short term scheduling I/O scheduling

what is the criteria for optimization based on the following: CPU utilization Throughput Turnaround time Waiting time Response time

Maximize CPU utilization Maximize throughput Minimize turnaround time Minimize waiting time Minimize response time

what is the purpose of the kernel?

Mediates access to system resources.

what are the five states of a process in the five state model?

New: A process that's been created but not admitted to the pool of executable processes Ready: A process that is ready to execute Running: The process that is currently being executed Blocked: A process that cannot execute until some event occurs Exit: A process that has been released from the pool of executable processes.

what is serial processing?

No operating system, user interacts directly with computer hardware. Explicit order in which operations occur and generally the results of one action are known before the next action.

What is the next generation of operating systems?

Parallel and distributed operating systems

what are users?

People, machines, other computers

what is hardware?

Physical components that provide basic computing resources

what are the two ways of implementing priority scheduling?

Preemptive scheduling method Non-preemptive scheduling method

what are the two ways of implementing scheduling algorithms?

Preemptive scheduling method Non-preemptive scheduling method

what are some things a process control block contains?

Process identifier Process state and priority CPU scheduling information Memory-management information I/O status information

what are the necessary parts to complete CPU scheduling?

Queues: ready queue, blocked queues, suspended queue CPU Scheduler Dispatcher module Scheduling algorithms

What are the two main problems of serial processing?

Schedule time: Most installations use a hard copy. Setup time: Includes loading the compiler and source program, saving compiled program.

What is priority scheduling algorithm?

Scheduler will always choose a process of higher priority over one of lower priority. An integer is associated with each process to tell its priority level with the smallest integer being the highest priority.

what is short-term scheduling?

Selects one of the processes from the ready queue and schedules them for execution. Executes most frequently.

what does CPU scheduling generally mean?

Short-term CPU scheduling

what are two attributes of non-preemptive scheduling?

Small overhead and low response.

what are application programs?

Software that defines how system resources are used to solve the computing problems of the users

what is the kernal?

The core of a computers operating system that has complete control over the computer and resides in a separate part of main memory. Its the first program to be loaded on startup.

what is response time?

The time between when a request is made to when a response is produced. Response time = (actual response time) - (request time)

what is the two state model?

There are two process states, running and not running. The OS controls the pattern of execution for processes.

why does a computer need an operating system?

To act as an intermediary between users and computer hardware.

what are the two variety states that a process may occupy any multitasking computer system?

Two-state model Five-state model

what is a time sharing method?

Used by OS to increase CPU utilization by allowing multiple jobs to share the CPU time equally. Allows multiple users access to the system at the same time

what is the operating system also considered to be?

control program: controls execution programs to prevent errors. resource allocator: manage all resources application program: control the execution of programs Interface between applications and hardware

what is turnaround time?

how long CPU takes to execute a process. Turnaround time = (time of completion) - (submission time)

what is CPU utilization?

how much time the CPU has worked in the total time CPU utilization = (execution time/total time) ×100

what are two attributes of preemptive scheduling?

it's a fast response and big overhead

what is CPU scheduling?

process of determining which process will have CPU for execution and which will wait

what might lower priority from priority scheduling suffer from?

starvation. Low priority processes may never execute. Solution is ageing, increasing priority over time.

what is a multiprogramming batch operating system?

the operating system first selects the jobs, and then begins to execute one of the jobs from the memory. When a job requires an I/O operation the operating system switches to another job

what is dispatch latency?

time it takes for the dispatcher to stop one process and start another process

what is long-term scheduling?

works with the batch queue and determines which programs are admitted to the system for processing. (New → Ready State) Objective is to provide a balanced mix of jobs to the short term scheduler