Notes

Operating system is a program that controls the execution of application programs. An interface between the applications and hardware.

- Manage system memory
- Manage processing tasks
- Handling input and output (I/O)
- Provides a user interface

- Multitasking
- Process threads that can be prioritized
- A sufficient number of interrupt levels
- Employed in a small embedded operating system that are packaged as part of micro devices like microprocessors.

Mainframe operating system
- An operating system on a mainframe computer, a powerful device used mainly by governments and businesses to process large amounts of information and support a great number of users

Embedded operating system
- An operating system is an optional part of an embedded device's system software stack, meaning that not all embedded system have one

In preemptive scheduling we preempt the currently executing process, in non-preemptive scheduling we can allow the current process to finish it's CPU burst time

In preemptive scheduling the process is forcibly sent to waiting state when a process with a higher priority comes to CPU, in non-preemptive scheduling the process at running state can not forced to leave the CPU until it is completed

Round-robin scheduling
- Each process get a small unit of CPU time called as time quantum, usual 10-100 milliseconds
- After this time has elapsed, the process is preempted and added to the end of the ready queue. Ready queue is treated as a circular queue.
- CPU scheduler goes around the ready queue, allocating the CPU each process for a time interval of 1 time quantum

Shortest Job First
- This algorithm associates with each process the length of it's next CPU burst
- When the CPU is available, it is assigned the process that has the smallest next CPU burst
- It is a non-preemptive policy.

FCFS (FIFO, Run-To-Completion, Run-Until-Done)
- The process that requests the CPU first is allocated the CPU first. It is a non-preemptive algorithm
- When a process enters the ready queue, its PCB is linked onto the tail of the queue
- When CPU is free, it is allocated to the process at the head of the queue

A device driver is a particular form of software application that is designed to enable interaction with hardware devices. Without the required device driver, the corresponding hardware devices fails to work. A device driver may also be called as software driver.

Plug and play is an ability of a computer to detect and configure a new piece of hardware automatically, without the requirement of the user to physically configure the hardware device with jumpers or dip switches.

- Ease, control, multitasking, speed, resources, scripting and remove access

Deadlock is a permanent blocking of a set of processes that either compete with system resources or communicate with each other. No efficient solution such as prevention, avoidance and detection.

- Deadlock occurs if P2 request R1. The reason is that R1 is currently owned by P1, but P1 requests R2 without releasing R1 first, so if P2 requests R1, a circular wait will form and both processes will be deadlocked.

- P1 requests and owns the file. P2 requests the file and is waiting for the P1 to finish or P1 releases the file, P2 owns the file. P2 release the file. No deadlock occurs.

- P1 requests and owns the tape. In the same time, P2 requests and owns the printer. Then P1 requests for printer but in the same time P2 requesting for tape. Deadlock occurs as the circular wait has formed

New - the process is accepted by the system and is placed in a queue
Ready - the process is ready to use, but is waiting for CPU
Running - the process is being executed by the CPU
Waiting - the process is blocked until the I/O device manager signals or the page fault handler signals
Halted - the process is terminated either because finishes successfully or it encounters unhandled error

- Foreground process has higher priority over background process

- Mutual exclusion, circular wait, no preemption, hold and wait

an operating system that guarantees a certain capability within a specified time constraint.

Objective of OS
Convenience - make computer user friendly
Efficiency - allows computer to use resources efficiently
Ability to evolve - constructed in a way to permit effective development

Smart card OS
- A program that runs processor embedded in smart card

Real time OS
- An operating system that guarantees a certain capability within a specified time constraint