Can you say all software which is necessary for a computer?
The only necessary software for a computer to operate is the
operating system. Everything else is software that you want to do
things with. Different people will want to do different things with
their computer, so what one person needs might be of no relevance
to another person. But without an operating system you cannot do
anything, as all the applications need that to run. If all you have
on your computer is an operating system, then there is not much you
can do with it, as you will then want applications. Even a lot of
the things that are shipped as part of the operating system, like
text editors, are not needed for the computer to function. Some of
these are known as utilities. So the operating system is the only
necessary software, and after that it is whatever you want to be
able to do with the computer that will determine what you deem to
be necessary.