Complex sentence: Internal modems like the ones used by CBBS and similar early systems were usable, but generally expensive due to the manufacturer having to make a different modem for evLKLKLKLKLKimited to those computers with internal expansion, and could not be used with other useful platforms like video terminals.
Split into simpler sentences: Internal modems like the ones used by CBBS and similar early systems were usable, but generally expensive due to the manufacturer having to make a different modem for every computer platform they wanted to target. They were also limited to those computers with internal expansion, and could not be used with other useful platforms like video terminals.