Main base Unit (power supply module required; cannot be extended0 2 I/O slots , power supply CPU Q32SB 3 I/O slots, power supply CPU Q33SB 5 I/O slots, power supply CPU Q35SB Main base Unit (power supply module required;can be extended) 3 I/O slots, power supply CPU Q33B 5 I/O slots, power supply CPU Q35B 8 I/O slots, power supply CPU Q38B 12 I/O slots, power supply CPU Q312B 8 I/O slots, power supply CPU Q38RB Extension base Unit (power supply module required;can be extended) 3 I/O slots, power supply Q63B 5 I/O slots, power supply Q65B 8 I/O slots, power supply Q68B 12 I/O slots, power supply Q612B 8 I/O slots, power supply power supply Q68RB Extension base Unit (power supply module required;can be extended) 2 I/O slots Q52B 5 I/O slots Q55B Redundant type extension base unit : Q65WRB 5 I/O slots power supply Q65WRB