Jerome Fine replies: If you can find the controller, you will probably also find that the RX03 (if I remember correctly) supports 22-bit addresses via the hardware registers. I never bothered, but the RL02 emulation might also support 22-bit address via the hardware registers. If I remember correctly, the DSD 880 did NOT support 22-bit address for either the RL02 or the RX03 emulation. However, it is quite possible if you are running the RT-11 RT11XM monitor to support a bounce buffer when the RX03 is being used. DEC never supported 22-bit addresses for its RX02 floppy, although, as mentioned above, the RXX.SYS could be modified to include a bounce buffer when 22-bit addresses were required. DEC also had both 18-bit and 22-bit controllers for the RL02 drive. Sincerely yours, Jerome Fine -- If you attempted to send a reply and the original e-mail address has been discontinued due a high volume of junk e-mail, then the semi-permanent e-mail address can be obtained by replacing the four characters preceding the 'at' with the four digits of the current year.