bind8 and bind9 installed on the same server: possible?

[hugo hugoo]

Dear all,
 
I plan to upgrade my nameservers from bind8 to bind9.
I guess I will encounter some compatibility problems notably in the layout of the zone files
 
- can anybody give me the point of attention for this upgrade? Your experience will be appreciated.
 
- is it possible to install bind9 without removing bind8 in order to could easily and quickly swith from bind8 to bind9 and vice versa?
 
 
Thanks for your support.
 
Hugo, 		 	   		  
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