Every tutorial on Linux-based partitioning schemes (or, just partitioning in general) will tell you that a PC can have either 4 primary partitions, or 3 primaries and 1 extended. They will all also tell you that Linux (in my case, Ubuntu) can be installed on either.

It's also come to my attention that it is not too atypical for FHS directories, such as usr/, tmp/, etc/, home/ or var/ to be mounted separately on other partitions.

Several questions I am unable to find the answers to, purely for my own edification: (1) By "PC", are we really talking about common PC disk types, like IDE or SATA? I guess I'm wondering why PC uses are limited to 4 primaries or 3 primaries + 1 extended

(2) I'm choking on some basic OS concepts: it is said that a partition can be mounted by a file system or an OS. So I assume this means I can somehow instruct Ubuntu to mount to 1 partition, and then any part of, say, ReiserFS, to be mounted to another partition? How?

(3)(a) What about creating swap partitions? Is there too much of a good thing with swap partitioning? If I have 4GB RAM over 320GB disk, what should my swap partition size be, and why? (3)(b) Are swap files the only way to create swap partitions? Wouldn't a Linux partitioning utility allow me to define a partition as being for virtual memory only?

(4) Why are partitions limited to being "mounted" by just OSes and file systems? Why couldn't I write a program to take up its own, say, 512 MB partition, and then have it invoked or uses by an OS installed on another partition?

Thanks for shedding any light here... not critical that I know this stuff, but it's got me thinking incessantly. And when I think incessantly, I...can't......sleep....