Laplink (sometimes styled LapLink) was a proprietary piece of software 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 or USB and a USB adhoc network cable.[2][3][4]
Traveling Software is now known as LapLink Software, Inc.,[5] and their main software is now the PCmover. With the demise of parallel ports on PCs Laplink no longer sells the traditional cable. Instead it has USB to hard drive, USB to USB and Ethernet to Ethernet cables.[6]
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.
The INTERSVR program in MS-DOS 6.0 can also use a LapLink cable.
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 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 |