about the pdp-11/83: swapping cpu and memoryboard does work, but the performance stays the same: none, because i still don´t have any system by now. there is a small difference: the run led stays off all the time, but the system ODT works fine. i suppose this is a problem of passing the signals, but this is only a vague guess. when i boot the TK50 2.11BSD tape, i can get the disklabel program loaded. it asks: Disk? when i try to access the disks, the system hangs. when i access rl(0,0) (RL02 disk drive0) the system just hangs, no response. when i access ra(0,0) (RD54 disk drive0) i get a "menu": d(isplay) D(efault) m(odify) w(rite) q(uit)? i can enter D, then it should write the defaults to the disk. after this i get: d(isplay) D(efault) m(odify) w(rite) q(uit)? i enter d (to see what the program did), and i get: type:MSCP disk:RD54 flags: bytes/sector:512 sectors/track:17 tr (it stops right after tr) i suppose the program is asking the controller about drive parameters, and that´s where it fails. i can wait for hours, i´ll get no response. i can use all the menu, except d=display. i thought that maybe one of the controlles is broken and causes trouble on the qbus (maybe the RL02 controller). is there a way to check all this stuff? i do have some "winchester" controllers for PC/ISA, i could check the disks on a linux pc, no problem, but i don´t want to overwrite something "digital"-specific that i could not restore. those RD54-disks are regular ST506-mfm, right? maybe i should "downsize" the system to the basic elements i need to get it running maybe there really is a bus problem. i´d try this configuration: mem - cpu - rqdx3 - tqk50 (top-bottom) would this be ok? or, instead of using RD54 disks, should i try to use the rl02 as "pair" (one swap, one systemdisk)? i think step by step checking the hardware is the only thing i can do to get the pdp up and running. have a nice weekend -- lothar btw: does anyone know a good book/link about system-architecture, specially harvard- architecture ?