What's your LASTDRIVE= line in config.sys look like?

I have LASTDRIVE=J

Should be fine then... are you loading guest high?

No, I even booted without config.sys and autoexec.bat. Weird thing though; when I run guest.exe from the floppy it doesn't find the drive, but when I run it from a directory on C:\ it detects the drive, but with the above mentioned invalid drive specification error.

Blavius wrote on 2024-08-25, 20:01:

No, I even booted without config.sys and autoexec.bat. Weird thing though; when I run guest.exe from the floppy it doesn't find the drive, but when I run it from a directory on C:\ it detects the drive, but with the above mentioned invalid drive specification error.

There might be other files that guest.exe needs in the same folder with it on C: that you haven't copied to the floppy, like an .INI or a .CFG.

Good point, I was missing the ini and ASPI drivers on my disk. They are on there now, and both cases now behave equally.

As I was suspicious the CF card might be causing issues, I disconnected it and only had the ZIP drive on the IDE cable. I tried both positions on the cable (it is a straight one, without a twist), I tried all jumper positions on the zip drive; master, slave, CS and no jumper at all. I rem'ed either ASPIIDE or ASPIATAP in GUEST.INI to see if by chance I have an ATA unit. Everything produces the same result:

GUEST.EXE successfully finds the ZIP 100 and mounts it to C:\
When I access C:\ I get a 'General failure reading drive A '

Getting suspicious of the drive, I changed ZIP disk, no change. Eventually I connected the CF card again, booted into Win95, and the ZIP works perfect - in windows :-s

Maybe my version of the Iomega driver tools is rotten. I have version 6, but maybe an older version would fare better? I'm grasping at straws by now...

I found the 5.4 version of the Zip floppy online (https://archive.org/details/iomega-zip-disk-floppy-v-5.4).
-Booted from a disk with dos7.0, without config.sys or autoexec.bat
-Put in Iomega floppy and ran guest.exe
-Iomega guest driver version 5.4. Zip 100 drive letter is D:\.
-dir d:
-General failure reading drive C
Actual drive C (the CF card) is accessible though

As a last hail Mary, I took a different Zip drive from my windows 10 rig to try that in the 486. This is also a Zip 100 ATAPI, but there is a slight difference. The one I had been trying has a three possible jumper positions: master, slave, CS. The sticker on the 'new' drive also indicates additional positions: master, slave, CS, master A, slave A,CS-A.
A bit of reading suggest that these are modes where the zip drive can act as a bootable floppy drive, but only if the bios supports it.

The normal slave and master positions again resulted in an access error- BUT setting it on 'slave-A' made it work! It nicely mounts as D:\ under dos with driver 5.4 and 6.0 and can be accessed normally. When I boot to windows 95 it now shows as a '3.5" floppy drive D:\' instead of a removable drive, but works normally.

So, if you ever want to run one of these drives in wonky PS/2 systems hunt for one that has this floppy capability. For reference:

Drive with floppy capability:
Model: Z100ATAPI
PN: 270928-003
Example: https://samplerzone.com/cdn/shop/products/zip … pg?v=1529600565

Model without floppy capability:
Model: Z100ATAPI ZIP
PN: 02844D02
Example: https://esaitech.com/cdn/shop/files/L11965255 … pg?v=1702454976

I think the clearest way to distinguish is to look at the drive label; the differences between the 'three position' and 'six position' are quite clear.