Err, the M9300 would go in the same place as a M930, i.e. the UNIBUS in/out dual connector group, usually at the top (A/B connectors) of a slot in a backplane, in either the first or last slot _of the entire UNIBUS_. As a UNIBUS in/out dual-width device, the M9300 does not have separate 'grant in' and 'grant out' pins - just _one_ pin for the grant; the pin will function as 'in' _or_ 'out', depending on whether the card in question (of whatever type) is placed in the first or last slot of the UNIBUS. The dual-width G7273 goes in the middle connectors (C/D) of an SPC/MUD slot, to jumper both bus grants (BG4-BG7) and also NPG, all of which have both an 'in' and an 'out' pin in SPC/MUD slots (look at the G7273, you'll see 5 pairs of pins jumpered together - 1 set on one side, NPG; 4 sets on the other, BR4-BR7). So an M9300 cannot replace a G7273: it's intended for use in an entirely different kind of connector group. You might want to read the UNIBUS description in one of the earlier versions of the "PDP-11 Peripherals Handbook", which explains how the grants work: basically, they are daisy-chained through every device, so if a UNIBUS SPC/MUD backplane (which can hold a UNIBUS device in every slot) has a slot which does not contain a device, you have to put something with grant jumpers in instead. Whether the jumper need to be BG4-BG7 _only_ (the little small grant jumper cards), or a G7273 (which _also_ jumpers NPG) depends on whether _that particular slot_ has had its NPG jumper (wirewrap on the backplane) pulled, or not - most backplanes come with jumpers on NPG on all slots, and you have to remove the jumper if a device uses DMA. (In the early days, most did not, which is why that was the default.) The device the M9300 was invented for was probably the RH11-AB, which is where one most often finds them. The RH11 is an UNIBUS device which is a MASSBUS controller; the RH11-AB has connectors for _two_ UNIBI (so one RH11-AB can be 'in' two PDP-11's at the same time; i.e. all the devices connected to that controller can be accessed from either machine). If it's only connected to a single CPU, though, what does one do with the second UNIBUS? That's where the M9300 comes in. It simulated the NPG-granting section of a CPU, and when jumpered to do that, it goes at the _start_ of a UNIBUS - e.g. the second UNIBUS in the RH11-AB. (Leave all the jumpers in, and it functions like an M930, and can go at either end). You can find a description of its use in the RH11-AB, as well as a description of how the M9300 works, in the "RH11-AB Option Description" document (available online), starting on page 4-32. I can't conceive of any use for one in most PDP-11's, though (outside an RH11-AB, of course). Noel