Hey SUMEDHE5DMS, Welcome to the Nokia forums!
If you are looking to compare the devices, you could use the 'compare' function on the Nokia website to compare multiple products.
I hope this helps!
SUMEDHE5DMS if you are very familiar with linux then in that sense N900 is better than N9 because N9 has aegis security system which makes N9's kernel not 100% open like N900 so you can not do all Linux command things on N9 which you do on N900
Perhaps it would be fair to mention Inception as a means of circumventing platform security upon the N9.
Inception currently works but it is cat and mouse game already as last month Nokia had blocked initial Inception version with software update and Nokia may release un-hackable aegis version with up coming pr 1.3 release
Doubt that they will have either the wherewithal or inclination to continue locking it down.