GPC is not a drop-in replacement for Borland's Turbo Pascal (R). Almost all BP language features are supported. Notable exceptions are the string format (as discussed below), or the Mem and Port pseudo arrays, though replacement functions for the latter on IA32 platforms exist in the Ports unit.
Almost all of BP's run time library is supported in GPC, either by built-in compiler features or in units with the same names as their BP counterparts.
For details about the compatibility, the few remaining incompatibilities and some useful alternatives to BP features, see the Borland Pascal chapter in the GPC Manual. (see Borland Pascal)