A system unit (SU) was the fundamental hardware building block of an 11/20 and many subsequent PDP's. It was a frame 16.5 inches by 2.25 inches that held 3 blocks of dual card sockets. Each socket block was nominally 5.25 inches by 2.00 inches and could hold four "dual" cards spaced at 0.5-inch intervals. Thus the whole SU could hold four "quad" cards plus two "dual" Unibus connectors in its four rows by six sockets. Later production included a double-wide system unit that could hold nine cards. Typical things that came built into one SU include 4kW (8kB) of core memory and RK05 disk controllers. There were also SU's that were pre-wired to hold four Small Peripheral Controllers (SPC's). Typical SPC's included single-line serial interfaces, and line-printer controllers. Think of the H906-D as an 11/40 or 11/45 without any backplane or cards. I think you could put that system into two H960 racks. Figure 1/2 of a rack for the 11/40, 1/3 of a rack for the TU10. RK05, PC11, TU56 each take up 1/6 of an H960. With MOS memory you should have plenty of room in the 11/40 frame itself for the necessary one-SU controllers for RK05, TU56. Especially if you take out the 2-SU frame that originally held the core memory. I'm not sure where you put the TM11, I never actually had a real one, just emulated controllers that fit in one SU. Probably 500 or 600 pounds. If you can, look for the older H960's with welded frames rather than pop rivets. carl -- carl lowenstein marine physical lab u.c. san diego clowenstein(a)ucsd.edu