Another Patricia! Welcome to the forum.
There's a page on the REB 1100 on our wiki:
https://wiki.mobileread.com/wiki/REB_1100
and another on the RB format:
https://wiki.mobileread.com/wiki/RB
Also check out this section of the forum:
https://www.mobileread.com/forums/forumdisplay.php?f=152