Definition
Preemption
Preemption means that a job may be interrupted before it completes and resumed later.
In scheduling notation, it is written as in the field.
Effect
Preemption changes the structure of a schedule. Without preemption, each job occupies one continuous processing interval. With preemption, a job may be split into several pieces, possibly on different machines when the model permits migration.
In fixed-interval scheduling, preemption is usually not part of the basic model, because each accepted job already occupies a fixed interval.