by Dinesh Thakur Category: Operating System

The real-time operating system used for a real-time application means for those applications where data processing should be done in the fixed and small quantum of time. It is different from general purpose computer where time concept is not considered as much crucial as in Real-Time Operating System. RTOS is a time-sharing system based on clock interrupts. Interrupt Service Routine (ISR) serve the interrupt, raised by the system. RTOS used Priority to execute the process. When a high priority process enters in system low priority process preempted to serve higher priority process. Real-time operating system synchronized the process. So that they can communicate with each other. Resources can be used efficiently without wastage of time.

RTOS are controlling traffic signal; Nuclear reactors Control scientific experiments, medical imaging systems, industrial system, fuel injection system, home appliance are some application of Real Time operating system

Real time Operating Systems are very fast and quick respondent systems. These systems are used in an environment where a large number of events (generally external) must be accepted and processed in a short time. Real time processing requires quick transaction and characterized by supplying immediate response. For example, a measurement from a petroleum refinery indicating that temperature is getting too high and might demand for immediate attention to avoid an explosion.

In real time operating system there is a little swapping of programs between primary and secondary memory. Most of the time, processes remain in primary memory in order to provide quick response, therefore, memory management in real time system is less demanding compared to other systems.

Time Sharing Operating System is based on Event-driven and time-sharing the design.

The event Driven : In event-driven switching, higher priority task requires CPU service first than a lower priority task, known as priority scheduling.

Time Sharing : Switching takes place after fixed time quantum known as Round Robin Scheduling.

In these design, we mainly deal with three states of the process cycle

1) Running : when CPU is executing a process, then it is in running state.

2) Ready : When a process has all the resources require performing a process, but still it is not in running state because of the absence of CPU is known as the Ready state.

3) Blocked : when a process has not all required resources for execution, then it is blocked state.

Interrupt Latency : Interrupt latency is time between an interrupt is generated by a device and till it serviced. In RTOS, Interrupt maintained in a fixed amount of time, i.e., latency time bounded.

Memory Allocation: RTOS support static as well as dynamic memory allocation.Both allocations used for different purpose.Like Static Memory, the allocation is used for compile and design time using stack data structure. Dynamic memory allocation used for runtime used heap data structure.

The primary functions of the real time operating system are to:

1. Manage the processor and other system resources to meet the requirements of an application.

2. Synchronize with and respond to the system events.

3. Move the data efficiently among processes and to perform coordination among these processes.

The Real Time systems are used in the environments where a large number of events (generally external to the computer system) is required to be accepted and is to be processed in the form of quick response. Such systems have to be the multitasking. So the primary function of the real time operating system is to manage certain system resources, such as the CPU, memory, and time. Each resource must be shared among the competing processes to accomplish the overall function of the system Apart from these primary functions of the real time operating system there are certain secondary functions that are not mandatory but are included to enhance the performance:

1. To provide an efficient management of RAM.

2. To provide an exclusive access to the computer resources.

The term real time refers to the technique of updating files with the transaction data immediately just after the event that it relates with.

Few more examples of real time processing are:

1. Airlines reservation system.

2. Air traffic control system.

3. Systems that provide immediate updating.

4. Systems that provide up to the minute information on stock prices.

5. Defense application systems like as RADAR.

Real time operating systems mostly use the preemptive priority scheduling. These support more than one scheduling policy and often allow the user to set parameters associated with such policies, such as the time-slice in Round Robin scheduling where each task in the task queue is scheduled up to a maximum time, set by the time-slice parameter, in a round robin manner. Hundred of the priority levels are commonly available for scheduling. Some specific tasks can also be indicated to be non-preemptive.

Types of Real-Time Operating System

1) Soft Real-Time Operating System : A process might not be executed in given deadline. It can be crossed it then executed next, without harming the system. Example are a digital camera, mobile phones, etc.

2) Hard Real-Time Operating System : A process should be executed in given deadline. The deadline should not be crossed. Preemption time for Hard Real-Time Operating System is almost less than few microseconds.

Examples are Airbag control in cars, anti-lock brake, engine control system, etc.

Difference between in GPOS and RTOS

General-Purpose Operating System (GPOS)
Real-Time Operating System (RTOS)
1) It used for desktop pc, laptop.

1) It applied for the embedded application.

2) Process-based Scheduling used.

2) Time-based scheduling used like round robin.

3) Interrupt latency is not considered as much crucial as in RTOS.           3) Interrupt lag is minimal, measured in few microseconds.
4) No priority inversion mechanism is present in the system.             4) Priority inversion mechanism is current.Once priority set by the programmer, it can’t be changed by the system itself.
5) Kernel operations may or may not be preempted.   5) Kernel operation can be preempted.

About Dinesh Thakur

Dinesh ThakurDinesh Thakur holds an B.SC (Computer Science), MCSE, MCDBA, CCNA, CCNP, A+, SCJP certifications. Dinesh authors the hugely popular blog. Where he writes how-to guides around Computer fundamental , computer software, Computer programming, and web apps. For any type of query or something that you think is missing, please feel free to Contact us.

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