Difference between RTOS and general OS ?

difference between rtos and os

what are the differences between RTOS and General OS ..??

help me pls

thanks,

Kishore Kumar M.S.

general os

The key difference between general-computing operating systems and real-time operating systems is the need for " deterministic " timing behavior in the real-time operating systems. Formally, "deterministic" timing means that operating system services consume only known and expected amounts of time. In theory, these service times could be expressed as mathematical formulas. These formulas must be strictly algebraic and not include any random timing components. Random elements in service times could cause random delays in application software and could then make the application randomly miss real-time deadlines – a scenario clearly unacceptable for a real-time embedded system. Many non-real-time operating systems also provide similar kernel services.

General-computing non-real-time operating systems are often quite non-deterministic. Their services can inject random delays into application software and thus cause slow responsiveness of an application at unexpected times. If you ask the developer of a non-real-time operating system for the algebraic formula describing the timing behavior of one of its services (such as sending a message from task to task), you will invariably not get an algebraic formula. Instead the developer of the non-real-time operating system (such as Windows, Unix or Linux) will just give you a puzzled look. Deterministic timing behavior was simply not a design goal for these general-computing operating systems.

On the other hand, real-time operating systems often go a step beyond basic determinism. For most kernel services, these operating systems offer constant load-independent timing: In other words, the algebraic formula is as simple as: T(message_send) = constant , irrespective of the length of the message to be sent, or other factors such as the numbers of tasks and queues and messages being managed by the RTOS.

Many RTOS proponents argue that a real-time operating system must not use virtual memory concepts, because paging mechanics prevent a deterministic response. While this is a frequently supported argument, it should be noted that the term "real-time operating system" and determinism in this context covers a very wide meaning, and vendors of many different operating systems apply these terms with varied meaning. When selecting an operating system for a specific task, the real-time attribute alone is an insufficient criterion, therefore. Deterministic behavior and deterministic latencies have value only if the response lies within the boundaries of the physics of the process that is to be controlled. For example, controlling a combustion engine in a racing car has different real-time requirements to the problem of filling a 1,000,000 litre water tank through a 2" pipe.

Real-time operating systems are often uses in embedded solutions, that is, computing platforms that are within another device. Examples for embedded systems include combustion engine controllers or washing machine controllers and many others. Desktop PC and other general-purpose computers are not embedded systems. While real-time operating systems are typically designed for and used with embedded systems, the two aspects are essentially distinct, and have different requirements. A real-time operating system for embedded system addresses both sets of requirements.-Wiki.Answers


Hope this helps..

**broken link removed**

difference between os and rtos

I think it will be helpful to you ....

Re: difference between rtos and os

1.The main difference between GPOS and RTOS is that the RTOS should be
deterministic

2.RTOS are scalable.Adding of required components are allowed in RTOS.Hence the size of the image of RTOS can be reduced upon the available memory.

3.Good RTOS never supports virtual memory . The applications are loaded entirely i.e. There is no demand paging.


these are the main differences

RTOS never hang-up while general OS can hang-up. Windows usually hangs-up!

hii yadavvlsi... RTOS also hangs if you dont use properly..In my case it happened... I was using FREE RTOS for UC3B0256 [AVR 32 bit]... Due to stack overflow my code hangs.. RTOS never hang up is wrong one...

Have you tried VxWorks..!

@yadavvlsi - I am working with vxWorks for last 5 years and yes i can write a simple application to hang the software.
@kandhu26 - Yes , u r partially true , RTOS can hang up -
1 . when ur critical section execution got corrupted memory slot
2. U r application directly accesses the resource when u r vxworks kernel actually want to use it , but as the kernel is very small , u don't need to think about those options - as they are practically almost impossible.

But u r application is a module in vxworks environment which can hang due to mishandling of exceptions or unavailability of resources or for other related reasons ... It is that how u r accepting and handling the exceptions and using the shared resources.

vxWorks gives you the freedom to make your application a softRTOS type system or as a hardRTOS type system , depending on how u r handling the exceptions.

The same way Mars mission also halted as there were an exception handling problem, but still it was considered as a hardRTOS system.

Hope it was ok with both of you , please reply.

Hi,
Can anybody pls suggest any good documents to study RTOS for beginners.


---danya----

Hi,

Please find the below attachment... I think this might be help full to you...

danya said:

Hi,
Can anybody pls suggest any good documents to study RTOS for beginners.


---danya----

Click to expand...

Got two beautiful ppts online ...hope will be helpful.... but they cover very basics ....

Hi,
thanks for your replies. Actually i need to study VxWorks RTOS. But i am a beginner to RTOS...So i need to start from the basics concepts.....

Danya ,
these are really helpful ....
for vxworks application programming - **broken link removed**
for kernel development programming - **broken link removed**

Regards,