Jerome Fine replies: As far as I understand, a 22 bit PDP-11/23 and all PDP-11/73 systems use the same memory as the uVAX-I. That would seem to indicate that the same backplane can be used for either CPU in a BA23 box. As for a uVAX-II, I can remember using the SAME box for BOTH a PDP-11/73 and a uVAX-II system at least 5 years ago. So I am NOT saying that there are no backplanes which can be used with only one of the microPDP-11, uVAX-I and uVAX-II systems, only that as far as I understand and based on my actual experience, all of the BA23 boxes that I have (and I probably still have at least a dozen) can run all three of the above CPUs. If I am correct, can Tony please verify my statement in the previous paragraph? Or anyone else as well since Allison may have additional information about special backplanes which can run only one of the three CPUs. So except for the 4 * 8 backplane from a BA23 with epoxy in the last three slots (and it can still run all three CPUs), I concur with what Tony has stated! 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.