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Operating Systems Chapter 5
Terms from Chapter Five of Operating Systems Concepts by Galvin, Silberschatz, and Gagne
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Computer Science
Undergraduate 3
02/10/2013

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Term
CPU Scheduling
Definition
Deciding which processes are executed by the CPU at a time.
Term
Thread Scheduling
Definition
Deciding which thread is executed by the CPU.
Term
CPU Burst
Definition
A time where the CPU is executing instructions and doing calculations.
Term
I/O Burst
Definition
A time where the process is getting input or giving output.
Term
CPU-I/O Burst Cycle
Definition
A mix of CPU bursts and I/O bursts.
Term
Short-Term Scheduler
Definition
The process of selecting which process the CPU needs to execute.
Term
Preemptive Scheduler
Definition
When the scheduler can interrupt executing processes to switch to another process.
Term
Non-preemptive Scheduler
Definition
When the scheduler only switches tasks when the process switches from running to waiting, or terminates.
Term
CPU Utilization
Definition
Keeping the CPU going at all times. Since there is always something to be done, the CPU should always be doing something.
Term
Throughput
Definition
Number of processes completed per unit of time, commonly seconds. A way of measuring work being completed.
Term
Turnaround Time
Definition
Time that is takes a process to complete from when it becomes ready.
Term
Waiting Time
Definition
Time spent waiting by a process.
Term
Response Time
Definition
How long it takes for the system to respond to input.
Term
First-Come, First-Served Scheduling
Definition
The scheduler executes the processes in the order they arrive. Can be very slow since small processes can get stuck behind larger processes, decreasing response time.
Term
Exponential Average
Definition
Used to measure the time for the next burst needed by averaging past bursts by the process.
Term
Shortest-Remaining-Time-First Scheduler
Definition
Exactly what the name implies. Can lead to starvation of larger processes.
Term
Priority Scheduling
Definition
The process with the highest priority goes first. Can also lead to starvation. Equal priority are served in first come, first served basis.
Term
Starvation
Definition
When a process doesn't get to execute because the scheduler never lets it.
Term
Aging
Definition
Helps the low priority processes eventually execute by increasing their priority as time goes on.
Term
Round-Robin Scheduling
Definition
Has a time quantum that determines how much time a process gets and then goes to the next process in the ready queue.
Term
Time Quantum
Definition
Time slice, small unit of CPU time.
Term
Multilevel Queue Scheduling Algorithm
Definition
Making different partitions for similar processes. The CPU then goes through the partitions, executing processes from each.
Term
Multilevel-Feedback-Queue-Scheduling Algorithm
Definition
Allows processes to move between queues, based off of how low it takes to execute.
Term
Contention Scope
Definition
Mapping threads to kernel threads.
Term
Process Contention Scope
Definition
Mapping user threads to kernel threads.
Term
System Contention Scope
Definition
Scheme that determines which kernel thread a kernel process should use.
Term
Homogeneous Processors
Definition
Processors in a multiprocessors system that are the same.
Term
Asymmetric Multi-Processing
Definition
One CPU cores handles all scheduling and gives other work to other processors.
Term
Symmetric multiprocessing (SMP)
Definition
Each processor is self-scheduling.
Term
Processor Affinity
Definition
Keeping a process on the same processor it is executing on.
Term
Soft Affinity
Definition
The process tries to stay on a certain processor, but will move to another if it needs to.
Term
Hard Affinity
Definition
A process will not migrate processors ever.
Term
Load Balancing
Definition
Attempting to keep the load even across all processors.
Term
Push Migration
Definition
The scheduling processor checks load balance and pushes processes from busy processors to less busy processors.
Term
Pull Migration
Definition
Idle processors pull processes from busy processors.
Term
Deterministic Modeling
Definition
Taking a given input of processes and finding which algorithm gives the fastest schedule.
Term
Queuing Models
Definition
Ways of modeling queuing times to find the shortest schedule.
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