From Matthew Fuller’s “BSD vs Linux”:

“[...]
There’re a lot of philosophical disparity between the Linux world and the BSD world. And there are a lot of expressions about it out there. One I particularly like goes something like:
BSD is what you get when a bunch of Unix hackers sit down to try to port a Unix system to the PC. Linux is what you get when a bunch of PC hackers sit down and try to write a Unix system for the PC.
Now, I like that quip, not because it’s some sort of absolute revealed truth, but because it gives a very good feel for some of the differences. The BSDs, in general, are very much more like traditional Unices than Linux is. A lot of that is because they’re direct-line descendants of the BSD from Berkeley, which was a direct-line descendant of the original AT&T Unix. Unix-the-trademark is a trademark of The Open Group, and Unix-the-code is owned by SCO, so one can’t actually say that the BSDs are really Unix (that’s the sort of statement that triggered the USL/UCB lawsuit extravaganza, in fact). But, in many ways, the BSDs are direct derivatives of traditional Unix.
That shows through in a lot of ways. It shows up in the design of the base system and the packaging of addons. It shows up in the partitioning of the mass storage. It shows up in a lot of details of the commands. And it shows up in the attitudes and reflexes and prejudices of the developers, which are reflected in the code and in the users.
BSD is designed. Linux is grown. Perhaps that’s the only succinct way to describe it, and possibly the most correct.

[...] “
A few useful links: