A parallel port is a type of socket found on personal computers for interfacing with various peripherals. It is also known as a printer port or Centronics port. The IEEE Standard 1284 standard defines the bi-directional version of the port.

• Byte Mode: Bidirectional Byte Mode
• Centronics:
• EPP: Enhanced Parallel Port
• ECP: Enhanced Capabilities Port
• IEEE Standard 1284: IEEE Standard Signaling Method for a Bidiretional Parallel Peripheral Interface for Personal Computers
• IEEE Standard 1284.3: Standard for Interface and Protocol Extensions to IEEE Std. 1284 Compliant Peripheral and Host Adapter Ports.
• IEEE Standard 1284.4 Standard for Data Delivery and Logical Channels for IEEE Std. 1284 Interfaces.
• HP Multiple Logical Channels protocol (MLC): HP Multiple Logical Channels Protocol.
• Nibble: Bidirectional Nibble and Channel Nibble

Traditionally IBM PC systems have allocated their first three parallel ports according to the configuration in the table below.

If there is an unused LPTx slot, the port addresses of the others are moved up. (For example, if a port at 0x3bc does not exist, the port at 0×378 will then become LPT1.) The IRQ lines, however, remain fixed (therefore, 0×378 at LPT1 would use IRQ 7). The port addresses assigned to each LPTx slot can be determined by reading the BIOS Data Area (BDA) at 0000:0408.

Bit to Pin Mapping for the Standard Parallel Port (SPP):

~ indicates a hardware inversion of the bit.