As a rule, an industrial computer will have similar I/O ports to a standard commercial PC, with serial ports and digital I/O being the only notable additions, whereas military computers will use the same data buses (LAN, USB, serial etc), but connectivity will be via custom lockable 38999 connectors, that have better EMC, shock and vibration properties.
In addition, filtered power supplies are often used to enhance EMC performance, and specialist data buses, such as MIL-STD-1553 or ARINC 429 may also be required on military PC.