Hello Vogons community!
I have been following this forum for a long time—practically every day—and have learned a lot from your discussions. Today, I want to contribute by sharing an interesting discovery.
I purchased this ISA USB Disk Card on AliExpress for about $33 USD, including shipping, and it arrived in Chile (Latin America) in about 10 days.

https://es.aliexpress.com/item/10050086376462 … ayAdapt=glo2esp

I specifically chose the "DOC disk starts DOS" option because I was curious about how my 386SX at 40MHz would detect the DiskOnChip (DOC) module. Here are my findings:
- The DOC loads its own BIOS on boot:
TrueFFS-BIOS -- Version 3.3.9 for DiskOnChip 2000 (V4.2)
Copyright (C) M-System, 1992-2000
- If an IDE disk (HDD or CF-to-IDE adapter) is present, the system boots from it,
- and the DOC appears as an additional drive (D: or E:, depending on the existing configuration).
- To boot from the DOC, the BIOS must be configured to set all HDDs to "NOT INSTALLED." If IDE disks are detected, the system will always prioritize booting from them.
- The DOC came preinstalled with MS-DOS 6.22 (English version), with no AUTOEXEC.BAT and a simple CONFIG.SYS containing only:
DEVICE=C:\CH375DOS.SYS @280 %0
- Booting from the DOC works correctly, and USB pendrives are accessible through CH375DOS.SYS.
Now, the critical issue:
- TrueFFS-BIOS is incompatible with Windows 3.11 (386 Enhanced Mode):
- Windows freezes randomly
- Data corruption occurs on the HDD/CF-to-IDE device
- Even after disabling Windows 3.11’s "32-bit file access," the system still crashes, and data corruption occurs.
- Removing the DOC chip from the ISA card stabilizes both DOS and Windows 3.11—even with 32-bit file access enabled in Windows.
- This confirms that the issue originates from TrueFFS-BIOS interfering with disk operations.
Has anyone encountered a similar issue with DOC and TrueFFS-BIOS on legacy systems?I'm very interested in discussing this topic and finding possible solutions or workarounds!Thanks in advance for your opinions and help!