alright, thanx everyone.

The size of my performa's hard disk is: 13 GB. (the orginal one died some time ago) It runs Mac OS 9.1

So the size of the hard disk probably be the troublemaker.

Upgrading to 7.5.5 wouldn't be a good idea as i read here.

What would be the best OS for Mr T. (4 Mb) then?

System 7.0.1?