Emu XL-7 & MP-7 User's Group

Yesterday, I started installing my xl-7 rom, but when I opened the mp-
7, I discovered that I have 2 mp-7 roms.  1 was in slot 0 and the 
second was in slot 3.  I looked closer and I saw that 1 is Rev A and 
the other is Rev B.  I could not install xl-7 rom, so I removed the 
slot 3 Rom and now it works fine.  So my Rev A rom is outside and what 
should I do with it???

What is the difference between Rev A and Rev B roms?  Are they the 
same????