Ctrl+Alt+Del works, and Windows reaches Program Manager
Day two. A new build went onto fresh chips, this time with the 2 MB memory board and the 287 maths chip fitted. Ctrl+Alt+Del worked now, over and over. My test program passed everything three times in a row, including the tests that really reset the CPU and come back.
Then Windows 3.1. Started the long way round, it made it to Program Manager in Standard mode and exited cleanly back to DOS. The normal way, WIN /S, just hung on a blank screen, and so did EDIT. Fractint complained that my video mode didn't exist. All three turned out to be the same bug, which I found in the emulator later that day: the VGA card's BIOS expects to hand some video calls back to a spot in the system BIOS where an IBM BIOS keeps its video code, and Atlas had nothing there yet. Plain WIN /S finally worked on real hardware a couple of weeks later, with M15.
The other surprise: HIMEM.SYS stopped the machine with an I/O channel check. I found that one the same day. POST had never written to the extended memory, so the first read of the memory board's parity RAM set off the alarm. The next build fills it in once at power-on. I still get an I/O channel check under HIMEM now and then on later builds, but that's a different bug, E1, and it's still open. Oh, and DOS thought it was midnight on every boot, because POST never read the real-time clock. That got fixed too.
