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. However, the MOS chips contain more functions, such as two programmable reload timers and a simple I/O shift register function. Furthermore, the MOS devices allow the direction (input or output) of all their I/O pins to be individually programmed. The 8255 I/O pins have only four programmable direction bits: one for all of Port A(7:0), one for Port B(7:0), one for Port C(3:0) and one for Port C(7:4).