ST-506 hard drive emulation

On Mon, 2005-07-25 at 22:03 -0400, Kelly Leavitt wrote: I'm not sure how complex such a box would be. I *think* an ST506- interface drive looks pretty much like a big floppy, just with more heads. Far as I know, it doesn't do anything intelligent on the drive itself, just responds to head select / step commands from the controller and reads or writes data. The bit I don't know is the nature of the data signal at the interface - it uses +/- signal lines for both read and write data. I'm not sure if that's an analogue signal or a digital one. I could imagine a device containing a pile of non-volatile memory in a row/column arrangement. There'd be a free-running counter to address the memory row and simulate the rotation of the drive (this would also drive the index line when at address 0). Then there'd be a second counter linked to the memory column and controlled by the step line on the interface, in order to simulate a drive track; this would also drive the track 0 line when at address 0. OK, that's only simulating a single head; but it just scales up with more memory planes to simulate more platter surfaces. I *think* that would be it; the controller writes the necessary bit patterns when doing a LLF of the drive to mark out sector boundaries, so I don't think there's a need to handle anything complex in the virtual drive. I believe an ST506 drive's purely a data store/replay device and it knows nothing of the actual data stored on it - most of the circuirty on board is presumably just motor control and head amplifiers / filters. I'd have no idea how to properly design something on a PCB that'd work though at the sort of necessary speeds without noise problems! But I think *in theory* it's probably not a difficult thing to design, and just needs a good electronic engineer to do the PCB work. Arguments welcome though :-) Yes we've been here before on this list - I think that was working out how to replace a ST506 drive with IDE though (which of course does know about sectors and stuff) - hopefully driving a pile of NVRAM as a linear sequence of bits is a lot easier. I'm got a few stockpiled at the museum, both for ourselves and for if anyone else needs one in an emergency - people locally seem to dispose of them quite often, so I just save what I can. Of course the majority of them are probably in a non-working condition anyway! cheers Jules