TIBConnection by default requires the Firebird/Interbase client library (e.g. gds32.dll, libfbclient.so, fbclient.dll,fbembed.dll) and its dependencies to be

installed on the system. The bitness between library and your application must match: e.g. use 32 bit fbclient when developing a 32 bit application on 64

bit Linux.
On Windows, in accordance with the regular Windows way of loading DLLs, the library can also be in the executable directory. In fact, this directory is

searched first, and might be a good option for distributing software to end users as it eliminates problems with incompatible DLL versions.
TIBConnection is based on FPC Interbase/Firebird code (ibase60.inc) that tries to load the client library. If you want to use Firebird embedded, make sure

the embedded library is searched/loaded first. There are several ways to do this:

Include ibase60 in your uses clause, set UseEmbeddedFirebird to true

On Windows, with FPC newer than 2.5.1, put fbembed.dll in your application directory

On Windows, put the fbembed.dll in your application directory and rename it to fbclient.dll
Pre 2.5.1 versions of FPC did not try to load the fbembed library by default. See FPC bug 17664 for more details.
An indication of which DLLs need to be installed on Windows (Firebird 2.5, differs between versions:

fbclient.dll (or fbembed.dll)

firebird.msg

ib_util.dll

icudt30.dll

icuin30.dll

icuuc30.dll

msvcp80.dll

msvcr80.dll
Please see your database documentation for details.