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3.4. Hard and Soft Real-Time

Finally, there are two different kinds of real-time scheduling. The Linux kernel, even at its most extreme, uses only soft real-time. This means that, while processor and other scheduling algorithms may be optimized to give preference to higher-priority processes, no absolute guarantee of performance can be made. A real-time kernel helps to greatly reduce the chance of an audio process running out of data, but sometimes it can still happen.
A hard real-time computer is designed for specialized purposes, where even the smallest amount of latency can make the difference between life and death. These systems are implemented in hardware as well as software. Example uses include triggering airbag deployment in automobile crashes, and monitoring the heart rate of a patient during an operation. These computers are not particularly multi-functional, which is part of their means to accomplishing a guaranteed low latency.