Laplink (sometimes styled LapLink) is a proprietary software that was developed by Mark Eppley and sold by Traveling Software.[1] First available in 1983,[1] LapLink was used to synchronize, copy, or move, files between two PCs, in an era before local area networks, using the parallel port and a LapLink cable or serial port and a null modem cable[2] [3] [4] or USB and a USB ad hoc network cable. Traveling Software is now known as LapLink Software, Inc.,[5] and their main software is now the PCmover.
LapLink typically shipped with a specialized cable, allowing two PCs computers to be linked together via the parallel port, establishing a direct cable connection. This so-called LapLink cable or null-parallel cable is capable of faster transfer rates than the traditional null modem serial cable. At the time, almost all PCs had a parallel printer port, but neither USB nor modern Ethernet was available.
A Laplink cable can be seen as a parallel equivalent to a serial null modem cable. Because of the higher bandwidth of the parallel port versus the serial port, a Laplink cable is able to transfer data more quickly.
The Interlnk program on MS-DOS can also use the Laplink cable.
With the demise of parallel ports on PCs, Laplink no longer sells the traditional cable.[6]
The cable used two DB25 male connectors, and was wired as below:
| D0 | 2 | 15 | Error | |
| D1 | 3 | 13 | Select | |
| D2 | 4 | 12 | Paper Out | |
| D3 | 5 | 10 | ACK | |
| D4 | 6 | 11 | Busy | |
| ACK | 10 | 5 | D3 | |
| Busy | 11 | 6 | D4 | |
| Paper Out | 12 | 4 | D2 | |
| Select | 13 | 3 | D1 | |
| Error | 15 | 2 | D0 | |
| Select In | 17 | 19 | GND | |
| GND | 18 | 18 | GND | |
| GND | 19 | 17 | Select In | |
| GND | 21 | 21 | GND | |
| GND | 22 | 22 | GND | |
| GND | 23 | 23 | GND | |
| GND | 25 | 25 | GND |