Boot from USB?

[Hans <hans.ullrich@loop.de>]

Hi folks, 

I was unaware, that a native installed linux is capable from booting at the 
USB-port! 

I put a harddrive with linux with a native installed linux (native means, the 
harddrive was built-in) in an usb-case and could boot from it. This was nice!
Thus some questions appeared:

1. Is this is normal standard behaviour and can this be confirmed?

2. Does such a booted linux behave as lin ux from built-in harddrive or is 
there something I should watch?

I am asking, because I have several harddrives with "built-in"-installations 
on it, but I have not enough computers. As I do not want to open my computers 
and exchange the harddrive for an upgrade, the idea is, to put these 
harddrives into an usb-case, boot these and upgrade it.

This would so much ease my work!

Question is, will this work or will the upgrade possibly destroy some 
configurations, because it is now an USB-drive?

If all this is normal standard, what is the technical reason for this? Is this 
because the kernel is using initramfs and when this is loaded, it is no 
matter, from where it is started? 

I would be happy, if you could enlighten me.

Best regards

Hans