Is it Compact Flash Industrial card ?
Does it work under Windows/Linux ?

what compact flash are you using?

Does your computer work correctly with HDD or with other CF cards?

Maybe it's not storage issue, but a ram/cache issue?

So today I tried the following:
I hooked the following to a same setup - Pentium 166 computer:
1) Old seagate 2GB drive which was in the 486 originally, with DOS 6.22 and bunch of games and few programs (all works okay with exactly the same configuration (and BIOS settings)) - primary slave
2) New CF card in Delock adapter - secondary master
3) WD 10GB drive with Win 98 SE from the P166 - primary master

Then I did the following:
A) Booted into Windows 98 SE
B) formatted the CF card drive (format E: /s) - there was already a 2GB partition
C) xcopied contents of original 486 2GB driveto CF card (xcopy D:\*.* E:\*.* /s /e /r /v /k /f /c /h)
D) Put the CF card drive back itno my 486 - system did not boot 😵
E) Booted DOS 6.22 disk 1 from A:\
F) Restored master bood record on C:\ (fdisk /mbr) - system again did not boot 😠

The drive is visible in BIOS okay, and the xcopy thing convinced me that it is rather a HW issue
The CF card I am using is this: Transcend Compact Flash, 133x, UDMA 4, MLC, ECC, 4GB

What else do you suggest I do?
I am thinking maybe trying this o a different I/O controller ISA card, or a different OS - FreeDOS, or as has been suggested, Win95

assasincz wrote:

What else do you suggest I do?

Personally, I would clear the whole partition information, not just the MBR.. 😀
https://en.wikipedia.org/wiki/Track0

Several special tools can accomplish this task (fdisk is not enough), I like S0Kill.
I can't predict how your card will react to that, though. I never killed a CF card with such a program before, however.
If you're worried, just try a smaller, older card instead. Say 256, 512, 2048MB or so.
These sizes are closer to what was common in the 486 days. Maybe these old LBA translation algorithms will work better with these.

Alternatively, you can also use IDEDIAG to find out a good drive geometry and enter the settings manually in the CMOS Setup.
(In theory, you can use any fictional geometry on flash media, as long as the total capacity is not exceeded.
That even worked in the 286 days with real mechanical IDE drives. Please never do run a Low-Level Format from CMOS Setup, though.
That did kill one of my flash cards once.)

Hi all,

I do have an update - several of you hinted at using industrial grade CD card, which left me intrigued.
So I bought one, specifically Transcend CF200I 4GB cardhttps://uk.transcend-info.com/Embedded/Products/No-521
And it worked, now all programs and games I tried so far loaded and are working fine.
I still get an odd copy/delete error when suffling larger packets of data around, though.
So a solution it is, be it quite pricey - I could get a 480GB SSD drive for the price of Delock adapter and two 4GB CF cards.

assasincz wrote:

I still get an odd copy/delete error when suffling larger packets of data around, though.

Please check CMOS Setup and change PIO from PIO4 to PIO2 or PIO0. PIO4 is buggy.
Also try enabling/disabling block mode, 32-Bit Transfer etc. if you can.