"Can do" vs "must do" is the key here. On a PCB, you "can" or you "may" perform advanced transmission line analysis upon your PCB traces. I don't think that a

"Can do" vs "must do" is the key here. On a PCB, you "can" or you "may" perform advanced transmission line analysis upon your PCB traces. I don't think that a project like this needs much more than a 2-layer board (so microstrips are definitely overkill), but that doesn't change the fact that PCB parasitics analysis is basically a solved problem today and available on a lot of software packages. Anyway, my overall point is that large contiguous blocks of PCB are easier than thinking about connector issues (or for the matter: being forced to solder and manage all those connectors or headers). Not only is it easier to go header-free (and use a larger PCB), its better engineering due to tighter specs and analysis available. ------------ Now a bit of connector doodads and having fun is probably fun and all. But a stackup of 9x PCBs is reaching the point of absurdity. I can't think of any good engineering reason to have so many connectors. That's 9-separate PCBs on this design, meaning at a minimum, 9-separate ground planes on this design. Is that... good engineering? I don't think so. Its horribly complex but for seemingly no appreciable reason. Maybe sound / analog circuits go on a separate board, but I'm not seeing any sound here... ------------ That being said: I agree that at 500kHz maybe this level of analysis is not needed. But... on the other hand... these 74xxxx chips all have 30ns rise/fall times, so its not outside the realm of reality to be running this computer at 5MHz or 10MHz or so, 10x to 20x faster. At those higher speeds, you'll possibly need to think about these issues a bit more (or perhaps... more appropriately I should say... the author of this project "could have" aimed at a higher-speed target if they so chose)