Discuss the components that differentiate RTOS and Normal OS.
Real TIme Computing:
A system is said to be real-time if the total correctness of an operation depends not only upon its logical correctness, but also upon the time in which it is performed. Real-time systems, as well as their deadlines, are classified by the consequence of missing a deadline.
RTOS:
A real-time operating system (RTOS) is an operating system (OS) intended to serve real-time application requests.
2. Interrupt Handlers and schedulers:
Key factors in a real-time OS are minimal interrupt latency and minimal thread switching latency; a real-time OS is valued more for how quickly or how predictably it can respond than for the amount of work it can perform in a given period of time.
Since an interrupt handler blocks the highest priority task from running, and since real time operating systems are designed to keep thread latency to a minimum, interrupt handlers are typically kept as short as possible. The interrupt handler defers all interaction with the hardware as long as possible; typically all that is necessary is to acknowledge or disable the interrupt
3.Intertask communication and resource sharing:
i]Temprarily masking interrupts
ii]Binary Semaphores
iii]Messsage Passing
4.Memory allocation is more critical in an RTOS than in other operating systems.
First, speed of allocation is important. A standard memory allocation scheme scans a linked list of indeterminate length to find a suitable free memory block.This is unacceptable in an RTOS since memory allocation has to occur within a certain amount of time.
The simple fixed-size-blocks algorithm works quite well for simple embedded systems because of its low overhead.
Real TIme Computing:
A system is said to be real-time if the total correctness of an operation depends not only upon its logical correctness, but also upon the time in which it is performed. Real-time systems, as well as their deadlines, are classified by the consequence of missing a deadline.
- Hard
- Missing a deadline is a total system failure.
- Firm
- Infrequent deadline misses are tolerable, but may degrade the system's quality of service. The usefulness of a result is zero after its deadline.
- Soft
- The usefulness of a result degrades after its deadline, thereby degrading the system's quality of service.
RTOS:
A real-time operating system (RTOS) is an operating system (OS) intended to serve real-time application requests.
Features of RTOS:
1.An RTOS has an advanced algorithm for scheduling. Scheduler flexibility enables a wider, computer-system orchestration of process priorities, but a real-time OS is more frequently dedicated to a narrow set of applications.2. Interrupt Handlers and schedulers:
Key factors in a real-time OS are minimal interrupt latency and minimal thread switching latency; a real-time OS is valued more for how quickly or how predictably it can respond than for the amount of work it can perform in a given period of time.
Since an interrupt handler blocks the highest priority task from running, and since real time operating systems are designed to keep thread latency to a minimum, interrupt handlers are typically kept as short as possible. The interrupt handler defers all interaction with the hardware as long as possible; typically all that is necessary is to acknowledge or disable the interrupt
3.Intertask communication and resource sharing:
i]Temprarily masking interrupts
ii]Binary Semaphores
iii]Messsage Passing
4.Memory allocation is more critical in an RTOS than in other operating systems.
First, speed of allocation is important. A standard memory allocation scheme scans a linked list of indeterminate length to find a suitable free memory block.This is unacceptable in an RTOS since memory allocation has to occur within a certain amount of time.
The simple fixed-size-blocks algorithm works quite well for simple embedded systems because of its low overhead.
Real time OS Examples:
http://www.chibios.org/dokuwiki/doku.php?id=chibios:documents 
http://en.wikipedia.org/wiki/Real-time_computing
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