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(Olivetti M24SP) WD1002S-WX2 recognizes hard drive sometimes as D instead of C

freakedenough

freakedenough

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Vienna, AT
Hi guys,

I have a strange issue with my Olivetti M24SP. Its WD1002S-WX2 Hard Disk/Floppy Controller sometimes recognizes the hard drive as drive D instead of C, causing problems during startup of DOS. Besides of the incorrect drive letter, everything else works fine.
I already replaced the BIOS battery with a new 3,6V NiCD cell because I noticed that date/time were incorrect after a while of not turing it on, but this didn't help. Any idea whats wrong?
I believe the jumpers are correct according to https://stason.org/TULARC/pc/hard-d...L-CORPORATION-Two-MFM-ST506-412-driv-222.html although I didn't touch them so they should be still factory-set by Olivetti - the previous owner was a woman which didn't use the machine that often and had other interests than IT and playing around with jumpers.

 
Last edited:
freakedenough said:
Its WD1002S-WX2 Hard Disk/Floppy Controller sometimes recognizes the hard drive as drive D instead of C
Click to expand...
An example of when I have seen the only hard drive become D: rather than C: is:

(In the following, I have left out the BIOS interface. It does not contribute to this particular discussion.)

At the hardware/physical layer:
- The floppy disk controller presents the first attached floppy drive as floppy drive 0 (floppy drive 1 for the second drive, etc.)
- The hard disk controller presents the first attached hard drive as hard drive 0 (hard drive 1 for the second drive).

When DOS boots, it assigns logical drives (A:, B:, C:, etc.) to the physical drives/partitions.

Early versions of DOS did the assignment differently to later versions. I think it may have been DOS 4 when the change was made.

In a system with three floppy drives in the system (the motherboard BIOS thinks there are three), and one hard drive, the assignment is:
Early DOS: Floppy drive 0 becomes A:, floppy drive 1 becomes B:, floppy drive 2 becomes C:, hard drive 0 becomes D:
Later DOS: Floppy drive 0 becomes A:, floppy drive 1 becomes B:, floppy drive 2 becomes D:, hard drive 0 becomes C:

Just now, on my IBM 5160, I got the one and only hard drive (DOS 3.3 installed) booting as D: by changing the floppy count switches on the motherboard from 2 to 3. (It is one of the reasons why when I attach a third floppy drive, an external one, I leave the floppy count switches set to 2, and load DRIVER.SYS for the third floppy drive.)

When I tried to access C: drive, I got a "Not ready error ..." message, not the "General Failure ..." message that you see. That suggests that 'motherboard BIOS sometimes thinks that there are three floppy drives' is not the situation that you are in. But, if you are in that situation, tools like CheckIt are expected to show three floppy drives (CheckIt 2.1 displayed "Floppy Drive(s): A:present, B:present, C:present"). Also, in the fault condition, you could try a floppy boot from say, DOS 6.
 
The 24(SP) battery is only for clock, nothing else.

Did you disabled onboard HDU support? Otherwise the onboard HDU bios may detects the drive first, and then the WD bios again...

m24hdu.jpg
 
Turning this switch off just gave me error1.jpg
error1.jpg

But in reverse and according to https://stason.org/TULARC/pc/hard-d...L-CORPORATION-Two-MFM-ST506-412-driv-222.html I removed the jumper from W3 (card BIOS OFF) on the WD card but turned the switch on the motherboard back on, which then gave me error2.jpg
error2.jpg

until I placed the WD card into slot 1 instead of 3 (from right), now it boots as regular and I can access both C and A.


Lets see how this turns out on a long term, I will update the thread later.

Thanks for your tip!
 
Checked again that thing. You have selected the dip switches to use the M24 internal HDU BIOS and not the one on the controller. When looking at the controller closely this is right, as the ciontroller has an empty ROM socket.

M24 BIOS is 1.43, that is the latest which is usually found. Currently I have no idea how that behaviour could happen. Maybe using some of system information tools to see what kind/size it detects for 1st drive? Maybe that gives an idea.

Anyhow, I have a 2nd idea to try. Get a WD 1002WX2 BIOS chip, plug it on the controller, enable it by controller jumper, and disable M24 HDU BIOS via mainboard dip switch. But maybe you have to lowlevel format and reinstall the harddisk. Maybe that fixes the issue by using different controller BIOS.
 
If anyone can read the assembler code, would be interesting. However, I meanwhile migrated to a self-soldered XTIDErev3 and will turn on the original hard disk only from time to time.
 
Apologies; I didn't realize the motherboard was exactly the same. I thought my 6300 WGS was the M24 SP equivalent (10 MHz 8086) but now I'm not so sure.
 
Trixter said:
XTIDE will perform better anyway, so no need to pursue it further. Remember to select the correct BIOS options for compatibility+speed.
Click to expand...
Thanks for the hint, but I already configured/flashed it for "XTIDE rev 2 (Olivetti M24)" in XTIDECFG of BIOS 2.0 from 2019 and it's noticably faster than the MFM.
 
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