Parallel data transmission will transmit multiple bits at the same time over multiple wires. This does allow faster data transmission rates, but the connectors and cables become much larger, more expensive and less flexible. These interfaces still use handshaking to control data flow.

These interfaces are common for computer printer cables and short interface cables, but they are uncommon on PLCs. A list of common interfaces follows.

Centronics printer interface - These are the common printer interface used on most personal computers. It was made popular by the now defunct Centronics printer company.

GPIB/IEEE-488 - (General Purpose Instruments Bus) This bus was developed by Hewlett Packard Inc. for connecting instruments. It is still available as an option on many new instruments.