The purpose of this document is to provide information on the PC-Doctor Parallel Port Loopback Adapter and Software Locking Device.
The blue parallel port loopback adapter operates as both a loopback device for parallel port testing and as a software locking device. The parallel port loopback adapter is designed to loop incoming data back to the parallel port and is necessary to run the External Read Test and External Write Test in Service Center for Windows and Bootable Diagnostics, or the Parallel Port External Loopback Test in Service Center for DOS. Attach the parallel port loopback adapter to the 25-pin parallel port before running these tests. The adapter can be seen below:
Only blue parallel port loopback adapters with a hologram on the top will function as a software locking device.