Top 10 List of Week 08
1.Preemptive Scheduling
Preemptive scheduling is used when a process switches from running state to ready state or from waiting state to ready state. The resources (mainly CPU cycles) are allocated to the process for the limited amount of time and then is taken away, and the process is again placed back in the ready queue if that process still has CPU burst time remaining. That process stays in ready queue till it gets next chance to execute.
2.Non-preemptive Scheduling
Non-preemptive Scheduling is used when a process terminates, or a process switches from running to waiting state. In this scheduling, once the resources (CPU cycles) is allocated to a process, the process holds the CPU till it gets terminated or it reaches a waiting state. In case of non-preemptive scheduling does not interrupt a process running CPU in middle of the execution. Instead, it waits till the process complete its CPU burst time and then it can allocate the CPU to another process.
3.Schedulers
Schedulers are special system software which handle process scheduling in various ways. Their main task is to select the jobs to be submitted into the system and to decide which process to run.
4.Long Term (Job) Scheduler
Due to the smaller size of main memory initially all program are stored in secondary memory. When they are stored or loaded in the main memory they are called process. This is the decision of long term scheduler that how many processes will stay in the ready queue. Hence, in simple words, long term scheduler decides the degree of multi-programming of system.
5.Medium-term Scheduling
Most often, a running process needs I/O operation which doesn’t requires CPU. Hence during the execution of a process when a I/O operation is required then the operating system sends that process from running queue to blocked queue. When a process completes its I/O operation then it should again be shifted to ready queue. ALL these decisions are taken by the medium-term scheduler. Medium-term scheduling is a part of swapping.
6.Short Term (CPU) Scheduler
When there are lots of processes in main memory initially all are present in the ready queue. Among all of the process, a single process is to be selected for execution. This decision is handled by short term scheduler.
7.Process
Process means any program is in execution. Process control block controls the operation of any process. Process control block contains information about processes for example Process priority, process id, process state, CPU, register, etc. A process can creates other processes which are known as Child Processes. Process takes more time to terminate and it is isolated means it does not share memory with any other process. The process can have the following states like new, ready, running, waiting, terminated, suspended.
8.Thread
Thread is the segment of a process means a process can have multiple threads and these multiple threads are contained within a process. A thread have 3 states: running, ready, and blocked. Thread takes less time to terminate as compared to process and like process threads do not isolate.
9.Uniform Memory Access (UMA)
In UMA, where Single memory controller is used. Uniform Memory Access is slower than non-uniform Memory Access. In Uniform Memory Access, bandwidth is restricted or limited rather than non-uniform memory access. There are 3 types of buses used in uniform Memory Access which are: Single, Multiple and Crossbar. It is applicable for general purpose applications and time-sharing applications.
10.Non-uniform Memory Access (NUMA)
In NUMA, where different memory controller is used. Non-uniform Memory Access is faster than uniform Memory Access. Non-uniform Memory Access is applicable for real-time applications and time-critical applications.