OS PROCESS SCHEDULING Flashcards
What is an operating system?
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
What are the main objectives of an Operating System
- Convenience
- Efficiency
- Ability to evolve
Draw a diagram showing the place operating systems occupy in the computer architecture
*See notes for pic
Give examples of OS services
- Program development
- Program execution
- Access I/O devices
- Controlled access to files
- System access
- Error detection and response
- Accounting
What is process scheduling
Process Scheduling is an OS task that schedules processes of
different states like ready, waiting, and running.
Give reasons why process scheduling is important
• Process scheduling allows OS to allocate a time interval of CPU
execution for each process.
• Another important reason for using a process scheduling system is
that it keeps the CPU busy all the time.
• This allows you to get the minimum response time for programs
What is the purpose of process scheduling queues
• Process Scheduling Queues help you to maintain a distinct queue for each and
every process states and PCBs.
• All the process of the same execution state are placed in the same queue.
What are process states and PCBs
• Process control block (PCB) is a data structure used by computer operating systems to store all the
information about a process.
• Information in a process control block is updated during the transition of process states
• Therefore, whenever the state of a process is modified, its PCB needs to be
unlinked from its existing queue, which moves back to the new state queue.
What are the types of operating system queues
- Job queue – It helps you to store all the processes in the system.
- Ready queue – This type of queue helps you to set every process residing in the main
memory, which is ready and waiting to execute. - Device queues – It is a process that is blocked because of the absence of an I/O device.
Using a diagram explain how process scheduling queues work
*See notes for pic
What are the Two-state process models
Running
• In the Operating system, whenever a new process is built, it is entered into the system, which
should be running.
Not Running
• The process that are not running are kept in a queue, which is waiting for their turn to execute.
Each entry in the queue is a point to a specific process.
Explain some important objectives of process scheduling
- Maximize the number of interactive users within acceptable response times.
- Achieve a balance between response and utilization.
- Avoid indefinite postponement and enforce priorities.
- It also should give reference to the processes holding the key resources.
What is a scheduler?
A scheduler is a type of system software that allows you to handle process scheduling.
What are the main types of process schedulers
Long term
Short term
Medium term
Describe long term schedulers
- Long term scheduler is also known as a job scheduler.
- This scheduler regulates the program and select process from the queue and loads them into memory for execution.
- It also regulates the degree of multi-programing.
- However, the main goal of this type of scheduler is to offer a balanced mix of jobs, like Processor, I/O jobs., that allows managing multiprogramming
Describe medium term schedulers
- Medium-term scheduling is an important part of swapping.
- It enables you to handle the swapped out-processes.
- In this scheduler, a running process can become suspended, which makes an I/O request.
- A running process can become suspended if it makes an I/O request.
- A suspended processes can’t make any progress towards completion.
- In order to remove the process from memory and make space for other processes, the suspended process should be moved to secondary storage.
Describe short term schedulers
- Short term scheduling is also known as CPU scheduler.
- The main goal of this scheduler is to boost the system performance according to set criteria.
- This helps you to select from a group of processes that are ready to execute and allocates CPU to one of them.
- The dispatcher gives control of the CPU to the process selected by the short term scheduler
What are the attributes of a process
The Process attributes refer to process characteristics such as data set size, kernel scheduling priority, the number of pages of memory, and the number of page faults.
