Worked a little on my custom XT clone. It is based on a "X'Golden board" https://dl.dropboxusercontent.com/u/107843342 … xt/IMG_0037.jpg (warning, 20Mpixel photo); originally came with a CGA card which I had hooked via composite video to a modern LCD TV since I don't have a CGA-capable monitor. Today I got to test a pile of VGA cards until I found one that works in a 8-bit slot (despite the card being 16-bit) - it's a OTI077-based card. None of the several Trident-based cards worked at all. I still have to test a Tseng 4000 card which I have hopes for.
The other thing I did was filling some of those empty EPROM sockets with some BIOS extensions. They are all mapped starting at F000:0000 in 8kB increments, i.e. take a 2764 chip each.
The first extension is a BIOS from a HD floppy controller, a KW-530 card; by that I enabled the XT to read/write 1.44M floppies (by default it can read/write only up to 720k floppies). I plugged in a UMC-based multi-IO card (again, 16-bit card in 8-bit slot) and verified that with the BIOS extension it can use 1.44M floppies.
Next I compiled a fresh binary of the XT-IDE Universal BIOS https://code.google.com/p/xtideuniversalbios/ and configured it so that it supports as primary IDE controller a 16-bit generic controller in 8-bit mode, and as secondary a XT-CF card https://www.lo-tech.co.uk/wiki/Lo-tech_ISA_Co … pter_revision_2 Then I verified that a CF card attached to either the multi-IO card's IDE connector or to the XT-CF card via a IDE/CF adapter works as a hard drive. It does, and now this XT clone has support for up to 4 HDDs and/or CF cards, not that I would ever need that many. I then installed MSDOS 6.20 on the CF card.
Everything works beautifully now.
My next plans for this machine are:
1. replace the 8088 CPU with a V20
2. add some memory in the HMA for UMBs and EMM. The motherboard has 640k onboard and no space for any extra. Currently in the HMA I have the VGA's video RAM and BIOS, which take up all the space from A000 to B7FF. The second half of the B segment, as well as the C, D and E segments are empty. I will add a AST Rampage 8-bit EMS card with 2M to make a EMS frame in the E segment, and then with a lo-tech RAM board https://www.lo-tech.co.uk/wiki/1MB-RAM-Board I will fill the C and D segments with 128KB RAM for UMBs. Too bad I can't use the second half of the B segment but this card can only map full 64kB pages.
(edit) Of course, replace HMA with UMA in all that I said above. This being a 8088 there is no HMA sadly.
I/O, I/O,
It's off to disk I go,
With a bit and a byte
And a read and a write,
I/O, I/O