What is the difference between Hard and Soft real-time systems?

- Real time operating systems are the systems that have been developed for serving to the real time requests of the applications. 

- They are readily capable of processing the data as it is inputted. 

- They do not make any delays in buffering. 

- Thus, the time taken for processing is quite less.

- The scheduling algorithms used by the real time operating systems are quite advance and dedicate themselves to a small set of applications. 

- Minimal thread switching latency and interrupt latency are two key factors of these kinds of operating systems. 

- For these systems the amount of time they take for responding matters more than amount of work they do.

- These systems are used to maintaining consistency in producing the output. 

The real – time operating systems can be divided in to two categories namely:

1. The hard – real time operating system and
2. The soft – real time operating system

In this article we discuss about these two systems and the common differences between them.

1. The hard real time operating systems produce less jitter while producing the desired outputs. On the other hand, the jitter produced by the soft real time operating system is quite more when compared to its hard real time counterpart.
2. The thing that distinguishes them is not the main goal but rather the type of performance it gathers i.e., whether hard or soft.
3. The soft real time operating systems have been designed as such that they can usually meet the deadlines whereas, the hard real time operating systems are designed in such a way so as to meet the deadlines deterministic-ally.
4. The hard – real time systems are also called as the immediate real time systems. They are bound to work within the confined strict deadlines. If in case, the application is unable to complete its task in the allotted time, then it is said to have failed. Some examples of the hard – real time operating systems are: anti-lock brakes, aircraft control systems and the pacemakers.
5. Hard real time operating system are bound to adhere to the deadlines assigned to them. Missing a deadline can incur a great loss. As for the soft real time operating systems, it is acceptable if the deadline is missed such as in the case of the online databases.

There is also a third category of the real – time operating systems that is not so known. It is called the ‘firm RTOS’. They also need to keep up to the deadline since missing it won’t cause any catastrophic effect but may give results that are undesirable.

More about Real time Operating System

- The embedded systems have evolved all of a sudden and now they are present all around us in digital homes, cell phones, air conditioners, cars and so on. 

- We very rarely recognize the extent to which they have eased our day to day life. 

- Safety is another aspect of our lives for which we depend on these embedded systems. 

- The thing that controls these systems is the operating systems. 

- Real time operating system is what that is used by most of these gadgets. 

- The tasks that are assigned to a real – time OS always have deadlines. 

- The OS adheres to this while completing it. 

- If these systems miss the deadline the results can be very dangerous and even catastrophic. 

- With each passing day the complexity of these systems is increasing and so our dependence on them.

- Some examples of real – time operating systems are:

Ø  OSE

Ø  RTLinux

Ø  Windows CE

Ø  LynxOS

Ø  QNX

Ø  VxWorks

- The RTOS know well not to compromise with the deadlines. 

What are Real-time operating systems?

- The RTOS or a real time operating system was developed with the intention of serving the application requests that occur in real time. 

- This type of operating system is capable of processing the data as and when it comes in to the system. 

- This it does without making any buffering delays. 

- The time requirements are processed in 10ths of seconds or even on much smaller scale. 

- A key characteristic feature of the real operating system is that the amount of time they take for accepting and processing a given task remains consistent. 

- The variability is so less that it can be ignored totally.

Real time operating systems also there are two types as stated below:

1. The soft real –time operating system: It produces more jitter.
2. The hard real – time operating system: It produces less jitter when compared to the previous one.

- The real time operating systems are driven by the goal of giving guaranteed hard or soft performance rather than just producing a high throughput. 

- Another distinction between these two operating systems is that the soft real time operating system can generally meet deadline whereas the hard real time operating system meets a deadline deterministic ally.

- For the scheduling purpose, some advance algorithms are used by these operating systems. 

- Flexibility in scheduling has many advantages to offer such as the cso (computer system orchestration) of the process priorities becomes wider.

- But a typical real time OS dedicates itself to a small number of applications at a time. 

- There are 2 key factors in any real –time OS namely:

1. Minimal interrupt latency and
2. Minimal thread switching latency.

- Two types of design philosophies are followed in designing the real  time Oss:

1. Time sharing design: As per this design, the tasks are switched based up on a clocked interrupt and events at regular intervals. This is also termed as the round robin scheduling.
2. Event – driven design: As per this design, the switching occurs only when some other event demands higher priority. This is why it is also termed as priority scheduling or preemptive priority.

- In the former designs, the tasks are switched more frequently than what is strictly required but it proves to be good at providing a smooth multi – tasking experience. 

- This gives the user an illusion that he/ she is solely using the machine. 

- The earlier designs of CPU forced us to have several cycles for switching a task and while switching it could not perform any other task. 

- This was the reason why the early operating systems avoided unnecessary switching in order to save the CPU time. 

- Typically, in any design there are 3 states of a task:

1. Running or executing on CPU
2. Ready to be executed
3. Waiting or blocked for some event

- Many of the tasks are kept in the second and third states because at a time the CPU can perform only one task. 

- The number of tasks waiting to be executed in the ready queue may vary depending on the running applications and the scheduler type being used by the CPU. 

- On multi – tasking systems that are non – preemptive, one task might have to give up its CPU time to let the other tasks to be executed. 

- This leads to a situation called the resource starvation i.e., the number of tasks to be executed is more and the resources are less.