Real-time computing processes data immediately, producing results without delay. Real-time systems must respond quickly and predictably, with hard real-time systems having strict deadlines. Failure to meet deadlines can cause system failure and loss of life. Soft real-time systems allow for some delays and are used in multiple connected systems or concurrent access requirements. Examples include anti-lock brake systems and travel schedule software.
In computer science, real time refers to a very short time interval, which appears to be immediate. When a computer processes data at this rate, it reads and manages the data as it is received, producing results without delay. For example, a website that is updated in real time will allow its visitors to see changes as they happen, rather than waiting for updates to appear at a later date.
A non-real-time computing process has no deadline. A real-time system, on the other hand, should respond not only quickly, but also within a predictable amount of time. A good example is a car’s anti-lock brake system. An anti-lock brake system is expected to release a vehicle’s brakes, preventing dangerous wheel locking, in a predictably short amount of time.
Unfortunately, there are times when real-time systems fail to respond as desired. Such a process fails when its task is not completed before its deadline. In computing, a grace period is not granted due to other requests on a system. Deadlines must be met regardless of other factors; they are considered mission critical.
When a process is considered hard real-time, it has to complete its operation within a specific time. If it misses the deadline, its operation is worthless and the system of which it is a component could fail. When a system is considered real-time soft, however, there is room for delays. For example, in such a system, one delayed process might not cause the whole system to fail. Instead, it can lead to a decrease in the normal quality of the process or system.
Hard real-time systems are often used in embedded systems. Consider, for example, a car engine control system. Such a system is considered difficult because a delayed process could cause the engine to fail. These systems are employed when it is critical that a task or event be handled within a strict deadline. This is typically necessary when damage or loss of life may occur due to system failure.
Real-time soft systems are typically employed when there are multiple connected systems that need to be maintained despite changing events and circumstances. These systems are also used when there are concurrent access requirements. For example, the software used to maintain travel schedules for major transportation companies is often real-time soft. It is necessary for such software to update programs with little delay. However, a few seconds delay is unlikely to cause confusion.
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