Complex sentence: The first five games in the series were written in Apple Pascal, an implementation of UCSD Pascal, and were ported to many different platforms by writing UCSD Pascal implementations for the target machines (Mac II cross-development).
Split into simpler sentences: The first five games in the series were written in Apple Pascal, an implementation of UCSD Pascal. They were ported to many different platforms by writing UCSD Pascal implementations for the target machines (Mac II cross-development).