Characteristics of real time operating system?

Answer 1

The unique requirements of real-time operating systems can be characterized by five general areas and are discussed below:

Determinism: Determinism is concerned with the time it takes, delay time, for an operating system to acknowledge an interrupt. An operating system is deterministic to the extent in that the performance of operations are at fixed, predetermined times or within predetermined time intervals.

Responsiveness: Responsiveness is concerned with the time an operating system services an interrupt once an acknowledgement is received. There are three aspects of responsiveness which include the following:

1) The time required to initially handle the interrupt and being execution of the interrupt service routine (ISR).

2) The time required to perform the ISR which is generally dependent on the hardware platform.

3) Since an interrupt can be affected by the arrival of another interrupt the nesting effect is of interest.

User control: In real-time operating systems, the users have find-grained control over scheduling task priority. The user must have a complete understanding between hard and soft tasks and to specify relative priorities within each class. Several characteristics may be available for the user to specify in these systems, such as, the use of paging or process swapping, what processes must always be resident in main memory, what disk transfer algorithms are to be used, the various processes' priority bands, etc.

Reliability: In comparison to non-real-time operating systems, reliability of real-time operating systems is far more important since the system is responding to and controlling events in real time. Performance degradation or loss thereof may have catastrophic consequences, ranging from financial loss to major equipment damage and even loss of life. Non-real-time systems include, but not limited to, transient failure and processor failure in a multiprocessor system.

Fail-soft operation: The characterization of Fail-soft operation refers to the ability of a system to fail in such a way as to preserve as much capability and data as possible. In a real-time system, the system attempts to correct the problem or minimize its effects while continuing to run. Stability is an important aspect of fail-soft operation, and an example of stability is provided for clarity purposes. In cases where it is impossible to meet all task deadlines, the real-time system remains stable while meeting the most critical, highest-priority tasks even if some of the less critical task deadlines are not met. The following features are usually included in real-time operation systems: fast process or thread switch, small size, ability to respond to external interrupts quickly, multitasking with interprocess communication tools such as semaphores, signals, and events, use of special sequential files that can accumulate date at a safe rate, preemptive scheduling based on priority, minimization of intervals during which interrupts are disabled, primitives to delay tasks for a fixed amount of time and to pause/resume tasks, special alarms and time-outs, etc.