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... is allowed, in view of circumstances outside the operation). Real-time operations require a stable system and are not necessarily fast. The polar opposite of a real-time operation is a batch job with interactive time sharing falling somewhere in-between the two extremes. Alternately, a system is said to be hard real-time if the correctness of an operation depends not only upon the logical correctness of the operation but also upon the time at which it is performed. An operation performed after the deadline is, by definition, incorrect, and usually has no value.
In a soft real-time system the value of an operation declines steadily after the deadline expires. (Real-time, 27 Apr 2005) Many real-time systems do not have a delay on the input data. In such systems Digital signal processing (DSP) system, the input and the output can be processed or generated continuously in the time it takes to input data. Consider an audio DSP example: if a process requires 2. 01 seconds to analyze or process 2. 00 seconds of sound, it is not real-time. If it takes 1. 99 seconds, it is (or can be made into) a real-time DSP process. (Real-time, 27 Apr 2005) Real-time systems are widely used in economy where they provide a real-time access to information or data. And as we all know, in economy increasing of speed access to information increases the competitiveness of the company. Real-time processing systems are new technologies and will improve during the next decades.
Gartner forecasts a fast increase and use of these real-time systems. As example: CMX-RTX (tm) is a real-time multi-tasking operating system for microprocessors, microcomputers and DSPs. It supports nested interrupts, is very fast at context switch, contains all CMX functions in library. It also also is a configurable, works as task management, event management, timer management, message management, etc. CMX-RTX has a full pre-emption and ability to have cooperative and time slice scheduling. Well, I think that question about kinds of operating systems is clarified now.
Lets talk then about memory protection in OS. Jon Stokes states The OS and system hardware not only cooperate to fool the user about the true mechanics of multi-tasking, but they cooperate to fool each running program as well. While the user thinks that all of the currently running programs are being executed simultaneously, each of those programs thinks that it has a monopoly on the CPU and memory. (Introduction to Multithreading, Superthreading and Hyperthreading, October 03, 2002) When we run a program it is the only program loaded in RAM and the only program executing on the CPU. The thing is that program believes it use the whole memory space and that the CPU is executing it continuously and without interruption. But it is not so.
In fact, program shares RAM with all of the other currently running programs, that is why it has to wait its turn to slice a piece of CPU time in order to execute. In such way work all the programs. For the following discussion lets define the term program. According to Introduction to Multithreading, Superthreading and Hyperthreading In most modern operating systems, what users normally call a program would be more technically termed a process. Associated with each process is a context, "context" being just a catch-all term that encompasses all the information that completely describes the process's current state of execution (e. g.
the contents of the CPU registers, the program counter, the flags, etc. ) So this process consists of threads, and each process consists of at least one thread: the main thread of execution. The process also may consist from many threads and each of them can have its own local context in addition to the process's context. In spite the fact that all threads are bundled into the single process they still save a certain amount of independence. This independence, when combined with their lightweight nature, gives them both speed and flexibility. It is very hard to fool a process into thinking that it is only one thread going. First and foremost, you have to ensure that when the currently executing process's time slice is up, its context is saved to memory so that when the process's time slice comes around again it can be restored to the exact same state that it was in when its execution was halted and it was flushed from the CPU to make room for the next process.
When the process begins executing again and its context has been restored exactly as it was when it left off last, it has no idea that it ever left the CPU write Jon Stokes. The procedure of flushing the CPU and loading the next process's context is called a context switch. Of course, the context switch for a multithreaded process will take a lot of more time than for an individual thread within a process. The fastness depends on the amount of hardware support for context switching and the type of context switch. A context switch for a multithreaded process can waste a lot of time and number of CPU cycles. Cutting back on context switches improves execution efficiency and reduces waste, as does the extensive use of multithreading since thread switches are usually faster than full-sized process switches. (Introduction to Multithreading, Superthreading and Hyperthreading, October 03, 2002) As for the memory protection.
The applications are put in slave mode due to the interdiction of critical commands execution in users mode. Such as context switching, etc. If application applies to the part of memory the access is allowed under the stipulation that this part of memory belong to this application. The access to other parts of memory for that application will be denied.
The full memory control is realized due to the memory configuration instructions (pointers of memory descriptors in Pentium processors). It is very important that OS use memory control for protection of all memory, which is used by its applications. Each application work in its own address direction. Such quality allows localizing errors in work of other applications and preventing the failure of whole system. Coupled with preemptive multi-tasking is memory protection, which means that the OS also makes sure that each program uses the memory space allocated to it and it alone. In a modern, preemptively multi-tasked and protected memory OS each program is walled off from the others so that it believes it's the only program on the system.
As I have already said, the OS consists of many different programs and applications. So how are certificated are protected in an OS? First of all there are patents. The original idea of the patent system was to stimulate innovation and research by awarding innovators and researchers with a time limited monopoly on their ideas in return for them disclosing those ideas to the public. The feared alternative was for this knowledge and innovation to be kept secret as trade secrets by the people and companies making them, and these great ideas then never reaching the general public to be built upon by others and through that generating even more wealth for society than otherwise would be the case. And I want to add that some researches concealed their inventions because they feared.
Now, some people think that the original idea was not as much to protect ideas from being used by others, but to encourage the publication of the ideas so others could use them. Christian Schaller said, We today face the risk of software patents being approved in the EU because not enough parliamentary members will be showing up to vote. Due to this it is important for those of us who oppose software patents to make sure EU parliament members see the damage software patents cause, so they realize it is important to be there to vote providing the needed absolute majority. But sending out a clear message is also important for the process of patent reform in the US and other places who have fallen into the trap of introducing them.
Big companies themselves develop the required software. But they can bye the license fro using the software from another producers. Pity but through inadvertence of authorities we have a situation described by the Christian Schaller. He states The job we need to do here is make sure Wall Street realizes that with the new generation of companies doing nothing but filing and buying patents, mostly of dubious quality and correctness, followed by going after the people with big pockets, software patents are a liability for the companies in the software industry, not an asset The day we make Wall Street see the true effect of software patents, that is the day they will start punishing the share price of software companies.
And that is the day I think we will see a lot of industry leaders feeling much more free to join us in our struggle to get software patents dissolved continued Schaller. Nevertheless, we all use patented programs which we can bye in every specialized shop, or download from Internet. I want to stop on the programs, which can be downloaded from Internet. Some of them are free. Sometimes the authors and creators refuse to make money on the software. The also are programs which have a trial period.
You can use such program for pointed period of time (usually 30 days) and then you can bye this program if you like. The functions of program became inaccessible after the expiring of trial time. Also exist such a nice thing as Demo versions of programs or demonstration versions. Usually such programs allow you to acquaint with the opportunities and nothing more. And then you again must expend money. Bibliography Jack Lo, Susan Eggers, Joel Emer, Henry Levy, Rebecca Stamm, and Dean Tullsen, Converting Thread-Level Parallelism Into Instruction-Level Parallelism via Simultaneous Multithreading, ACM Transactions on Computer Systems, August 1997, pages 322 - 354.
Susan Eggers, Hank Levy, Steve Gribble. Simultaneous Multithreading Project, University of Washington Neal Stephenson, In the Beginning... was the Command Line, 1999 Real-time, 27 Apr 2005. Retrieved May 8, 2005 from web Jon Stokes, Introduction to Multithreading, Superthreading and Hyperthreading, October 03, 2002. Retrieved May 8, 2005 from web Christian Schaller, The argument against software patents, April 19, 2005.
Retrieved May 8, 2005 from web
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Research essay sample on Software Patents Real Time
