What's inside the PLT? Is it a Linux box?

Yes, it's a Linux box.  We run a hardened version of Linux to make the box less vulnerable to power failures.  There is also hardware inside to provide lots of USB ports for accessories like scanners, label printers, marking lasers, cameras, etc.  The simplest way to think of the PLT is probably to imagine a single box with the following inside:

1. Variable power supply unit (PSU) to power the device under test (DUT)
2. J-Link or similar firmware flasher
3. Digital Multimeter (DMM)
4. Linux computer