Not if you have to pay for the OS
That really depends what operating system you are talking about. You may want to clarify what operating system you are interested in. The source code of many commercial operating systems, such as Windows, is not freely available, so the answer is simply "you can't". However, the source code of other operating systems, such as the different Linux distributions, is available for free, and may even be modified legally. Please note that any operating system used in "real life situations" is a huge project; finding your way around the source code may be a daunting project. According to the Wikipedia, "As of 2013, the Linux 3.10 release had 15,803,499 lines of code." At 60 lines per page, that would be a quarter of a million pages, or about a thousand volumes, if it were to be printed.
The source code is freely available, in accordance with the licence agreement.
Conventional source software is the software which is not freely available that is the source code is not freely available to execute in various systems and the distribution of software is not allowed and there is no copy right for this type of software because the developer does not give the access rights to any other person other than the developer team. Conventional software is a very confidential one which is used for specific purposes, if distribution of this software is allowed then there will be no meaning of security.
It must be freely distributed without restriction and the source code must be available.
Freely distributable Unix/Linux systems come with the source code, which can be modified. Proprietary Unix systems are distributed as binary only, with no source code, so you can't modify the system (easily). Other reasons are legal: the proprietary systems are copyrighted, and the freely distributable versions should not have any copywritten code in them, thus allowing them to be distributed without licensing arrangements.
An open system is an operating system that is entirely free to use, copy or pass on to others. Linux Mint and Ubuntu are just two examples of many that are freely available for downloading from the internet.A proprietary system is an operating system that has to be paid for, has to be registered, and is never yours to own, copy or pass onto others. Microsoft's Windows is an example of proprietary systems software.
ShareWare and Open Source software are two types of software that are freely distributed.
In one of two conditions:public domain code - anyone can do anything they want with this sourceopen source code - this source is legally copyrighted, but distributed with a licence controlling how you can modify and redistribute
There are many advantages to using animal waste as an energy source. The most obvious advantage being that it is freely available.
When resources are not freely or abundantly available you say they are scarce or limited.
Yes. The source code for Open Office.org is freely available. You can download it, modify it and compile it but you are not permitted to sell it as stipulated in the GNU license agreement.
Yes, provided the source code of the changes is published freely and that the open source licence is applied to the code changed.