Hi, Great, thanks for the info. I'm sourcing a few S100 protoboards, so I'll be able to wirewrap a board with all the relevant RAM, ROM and I/O. I'll probably use later generation chips such as 62256 for RAM and 6264 for ROM. I can then put in the 8251 and 8255 for serial and parallel ports, respectively. Is that heresy in regards to these old boards? It's not an issue to me starting ROM at 0000h. I've written a few 8080 debug/monitors for my old Multibus stuff so I can always use one of these - or mod it accordingly. I've only got a 6-slot motherboard and a Northstar ZCB processor board, S100 ROM board and some Dynabyte RAM boards and I was going to use the motherboard and original S100 boards with this system. This means the 8800CPU board will be in a small 2-slot system - the CPU board and the RAM/ROM/IO board I'm going to make. I'll check the MWRITE signals and see what I can do, or if you have the info then that's even better. Just one more thing.... I suppose it's possible to use the 8800CPU bd without the power regulation components if I ensure the correct voltages go through the correct pins on the bus. I can then use an old spare PC power supply, instead of creating a new supply. Naturally, this would entail that no other S100 board can be used due to their on-board regulators. This isn't an issue if I build my own S100 boards, without regulation, for this system. Again, thanks for your help. This is my first foray into S100 stuff, and makes a nice change from Multibus. rgds river