It is a 16-channel data acquisition probe with 2 clocks, 1 qualifier and 1 external trigger input.
Note from operators manual:
You cannot mix P6442 probes with P6443 or P6444 probes to take an acquisition.
If you acquire data on P6442 probes at the same time you try to sample data on P6443/P6444 probes, the acquired data from the P6443/P6444 probes will be invalid.
Two versions exist, one has a removable cable and a different probe socket. The internals are exactly the same for both version though. The removable cable version was made before 1991 and the fixed cable after 1991.
The probe connectors have a 430 Ω resistor inline with the connector.
The pin-out of the probe is given. (looking from the front)
Thanks to Keith Neufeld for the pictures!