Complex sentence: All of these chips were originally available in a 40-pin DIL package but the i8255 provides 24 usable I/O pins whereas the MOS chips only provide 16 I/O pins plus 4 control pins.
Split into simpler sentences: All of these chips were originally available in a 40-pin DIL package. The 8255 provides 24 usable I/O pins whereas the MOS chips only provide 16 I/O pins plus 4 control pins.