I have a set of five RX50 floppies which contain various service tests. I have not yet discovered what machine/CPU these work upon. Could anybody point me in the direction of how to interpret the seven-character part numbers? All have a copyright date of 1983. They are as follows: CZUFDB1 (disk part # BL-T540B-M1 "USER TESTS") CZXD1B1 (disk part # BL-T541B-M1 "FIELD SERVICE TESTS 1") CZXD2B0 (disk part # BL-T542B-MC "FIELD SERVICE TESTS 2") CZXD3B0 (disk part # BL-T565B-MC "FIELD SERVICE TESTS 3") CZXD4B0 (disk part # BL-T583B-MC "FIELD SERVICE TESTS 4") Are these some version of XXDP? They came with the MVII and MicroPDP-11/73 systems that I got as part of The Great Haul back in July 1998, but there is no indication who they go to. I stumbled across something about deciphering those CZX-type numbers a while back but did not retain the URL (naturally, now that I need to use it). Thanks much. -Chris F. NNNN Christian R. Fandt, Treasurer Antique Wireless Association, Inc. Jamestown, New York USA email: cfandt at netsync.net Electronic/Electrical Historian URL: http://www.antiquewireless.org/