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Pentium PS/2 "NO OS" when trying to boot a clone of HD

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First post, by rbgrn

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Here's everything I know:

I have an old PC with failing on-board video (486sx25) that can't accept another video card b/c of BIOS limitations (I know about XT-IDE but I have 3 slots total and need industrial interface cards in it) so I thought I'd move it over to a Pentium 100 IBM PS/2 that I have, which has 4 ISA slots and 3 PCI so all good. I had previously cloned the HD to an industrial CF card (WD SiliconDrive) and this booted up just fine on the 486 as well as in virtualbox on my desktop. When I try to boot the same image on the IBM, I get "NO OS". When I plug in the original hard drive, it boots (but has some performance issues it seems like it feels like it's running at 8mhz). The OS I need to run on this is Xenix b/c this is for an industrial application. Using a FlashFloppy Gotek, I can boot FreeDOS, Linux and Xenix without issue. It sees the CF as a hard drive and I can boot into linux from a floppy, mount the CF and read/write it without issue. I can even write a FreeDOS image to the CF and it'll boot that. It just fails to boot when I write the Xenix image, even if I boot into linux and DD if=/hda (Original spinny HD) of=/hdc (CF) - that completes 100% but then I get "NO OS" when I try to boot off of the CF. It's a byte-by-byte copy...

Any ideas? Next week I'm switching to an industrial P4 board which I've heard work better for this but I would really like to know why this will boot off of anything except what I need.

Reply 1 of 5, by Horun

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I have no clue other than the IBM has an issue booting from a CF. Have you tried booting the IBM off any other CF card ?

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 2 of 5, by rbgrn

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Just tried this on a P4 board and found that it's not specific to the IBM - It's everything to do with Xenix... This xenix clone will boot on the original PC and in Virtualbox under every configuration I could try, but doesn't seem to like other PCs. I was able to boot other OSes off of the CF card so it's not that. Xenix unfortunately doesn't give me any real information as to why it won't pull up the bootloader but it's feeling like a geometry or device path thing to me.

Reply 3 of 5, by rbgrn

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Figured it out. The original drive (Maxtor 7131AT CHS 1002/8/32) has its geometry stored somewhere either in boot configuration or kernel configuration. When cloning, I had to use that CHS for the original drive and the CF drive's CHS is 1011/16/63. After cloning and booting from the CF, on this PC specifically I had to put in the original maxtor's CHS of 1002/8/32 for it to work. I don't know enough about how the Int 13H geometry works in interaction with this old Xenix version but I have it working using the original drive's geometry, not the actual geometry of the CF clone... that makes no sense to me personally because I would figure it would result in overlapping or missing sectors but whatever.

Reply 4 of 5, by megatron-uk

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Wow, Xenix actually being used for something!

I always assumed Microsoft pushed it to market and let it wither and die... I'm especially intrigued that it was in use on something as 'late' as a 486. I would have thought one of the BSD's or similar would have been used for something industrial by that time.

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Reply 5 of 5, by rbgrn

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I'm actually running it on a pentium 4 with isa slots for legacy support!

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