> This is probably a stupid question but here goes anyway. I have a Delphi application that is currently running on FB1.5. I need to move to FB2.5. Is it necessary to update the FB client on the client PC's from 1.5 to 2.5 or is the 1.5 client compatible with the 2.5 database?
> I have found that PCs that have the 2.5 client installed connect happily to a 1.5 database.

A 2.5 client accessing older Firebird server versions should be fine,
but I wouldn't recommend doing it the other way round. While it might
work (if at all?) to access a 2.5 server with a 1.5 client (although the
local protocol changed so you won't be able to use local connections),
you lose some stuff like the improvements in the remote protocol in the
Firebird client in 2.x etc.

--
With regards,
Thomas Steinmaurer (^TS^)
Firebird Technology Evangelist

http://www.upscene.com/
http://www.firebirdsql.org/en/firebird-foundation/