The Loopback Adapter Set includes:
Serial Port Loopback Adapter
The green serial port loopback adapter is necessary to run the Serial Port Loopback Test in Service Center for Windows and the Serial Port External Loopback Test in Service Center for DOS.
Audio Ports Loopback Adapter
The black audio ports loopback adapter is necessary to run the Rough Audio Test in Windows.
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. Some older units do not recognize USB devices as a bootable device, which would prevent you from running Service Center for DOS. If necessary, you can use this adapter in place of the Multipurpose USB Device to run Service Center for DOS.
Network Loopback Adapter
The blue network loopback adapter is required to run the Network External Loopback Test in Windows.