EXS 24 Logic Sampler Users Group

PC. WIN 2K. LOGIC PLAT' V5.1.
Hi all,
Just purchased the EXS24 for Logic.
Can anyone advise me about the following.
When openning the sampler instrument folder say for pianos I get 2 of 
the same file eg: Stereo Piano exs. and Stereo Piano.ECO. What does 
ECO stand for? Can I delete one of them as I find having 2 of the 
same file makes the list a lot longer. 
Many thanks,
Allan