I know theres the XTIDE (or something) project over at vintage-computer.com.
They sorta made these "kits" for 8 bit IDE controllers.

I'll find you a link, one sec...

Edit:
Heres the link:
http://www.vintage-computer.com/vcforum/showw … e=XTIDE+project

Forum member Chuck(g) over at vintage-computer.com is working on a modification of XTIDE that should allow you to use a regular 16-bit multi I/O card and a compact flash module (does not work with regular PATA HDDs or CD-ROMs). All you will need is a socket on the motherboard or expansion card to place the ROM.

Certainly, technology now would allow you to combine a lot of stuff on one card now; you'd mostly be limited by the space for connectors.

I'm interested in building something eventually. Maybe a memory board; those shouldn't be too hard. You can get huge static rams (16 meg for $15) now, which would be relatively easy to interface to. Its too bad the demand for all this is so tiny. Costs go down with quantity, but would you ever sell 100 of them?

There are probably not enough members on the board to do a group buy for 100 parts. How much would it cost per board at that quantity? I'm guessing the design would not be trivial, but then I'm not a EE so maybe it wouldn't be an issue for someone with those skills.

It would probably cost 30 or 50 for the parts, but assembling ranges from "free" if you do it yourself to several hundred bucks a board if someone did a small quantity. I don't think a company would bother producing less than a few hundred of an item unless the margins are really high.

Its worth remembering how expensive this stuff was.. an Aboveboard with 2 megs of ram was something like 2 grand.

Also, there's the software.. maybe you could emulate some old device with good drivers. Writing new drivers would probably take more time than designing the board, by a lot.

One comment on your 8 bit board.. The XTs would appear to be limited to 1 meg of ram (640 usable), but expanded memory would let you go to 32 megs. The expanded memory spec could be bent a little and go to a gig with very little trouble, and I think some of the newer FreeDOS type tools can do it. Expanded memory is limited in what you can do (generally its much easier to use for data than code space) for example Windows 3 and later won't run out of it, but you can use it for a disk cache and RAM drive.

For 8 bit boards, is there usually room on the motherboard for a 16 bit connector to hang out? I seem to remember some cards being able to operate as 8 or 16 bit cards. If you were designing something new for the retro crowd, that would be a good feature.

Even if it would be too expensive to do a limited run of boards, if this was something you could build relatively easily from plans, I could probably build one provided it didn't require anything more exotic than a soldering iron and voltmeter. If we start talking FPGA programmers and all that, it would be out of my league. Unfortunately, I don't have the skills to do the design work.

What would be awesome is if it could have say 16mb of EMS, maybe some I/O ports (2 serial 1 parallel). Not sure what else to put on it without making it crazy difficult. 16bit ISA card but option for 8bit only.

I think just a plain static ram, system memory board would be well within hobbyist soldering range. The comm ports too, though I don't know much about them. As long as its just some decoders hooked up directly to the devices, and all the chips are available in something you can solder, it would be feasible.

The EMS function would pretty much require an FPGA or other programmable device. EMS maps the big RAM space on the card to several small 16k windows in the top 384k of system memory. Not rocket science, but the address translation is probably going to become more than you can do with a handful of TTL chips.

Along these lines, does anybody know how the BIOS discovers the RAM on an expansion board? I've looked all over and not found much. Its almost like people aren't building ISA memory cards anymore! My guesses are:

1) An option ROM is picked up by the BIOS (the BIOS scans for these) and the ROM registers the memory with the main BIOS, through some interrupt call I haven't found yet.

2) The BIOS scans for more memory past the end of the system RAM and if it finds something, it keeps going?

Any ideas?

#1 complicates the DIY board; would require the board to have a ROM/EEPROM etc, and to write the program for it. I do have an EEPROM programmers, though..