M321 BIOS HD limitation question

Discussion about old PC hardware.

M321 BIOS HD limitation question

Postby Jed118 » 2018-2-09 @ 04:38

OK so I've got my 486DLC running ("running") again and I am preparing for my SCSI2SD to arrive. In the meantime, I'm playing around with a Seagate ST5850A that's in there now and while I can see the BIOS recognizes the drive as an 815Mb drive, DOS simply won't do it. I have purchased a 512 Mb CF card for this particular computer (despite my issues with CF, I will persevere as I do want to remove moving bits from this machine as much as can be allowed) so that's not really an issue, but I'm perplexed as to why DOS sees it as nothing more than a 528Mb drive.

This is the largest, non SCSI drive that I've put in there (the outgoing drive was an IDE Quantum 540Mb - 528Mb usable) but the same ST5850A drive is seen by my 486 (in DOS, as well as BIOS) as a proper 850Mb unit. I haven't compared the CHS settings between the two machines in BIOS as of yet, however, what is the deal here? IIRC if the BIOS can recognize the drive using the proper CHS parameters and reports its size correctly, why is DOS having an issue with it? I BIOS low-leveled the drive (because it had OnTrack on it) and reformatted it, and it still sees it as 528Mb in the M321 386.
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Re: M321 BIOS HD limitation question

Postby Jo22 » 2018-2-09 @ 08:43

It's a limitation of both BIOS/IDE specs.

With 512 bytes per sector, this results in the famous 504MB limit.

The reason why the BIOS shows the real capacity,
but can't use it is also related to this.

http://web.inter.nl.net/hcc/J.Steunebrink/bioslim.htm
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Re: M321 BIOS HD limitation question

Postby Jed118 » 2018-2-09 @ 12:25

Blast... I suppose I could try to find a BIOS update... Thanks for the read, it jogged my memory of these issues, which I haven't encountered in 10+ years ;)
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Re: M321 BIOS HD limitation question

Postby derSammler » 2018-2-09 @ 14:02

You can use Drive Overlay Software.
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Re: M321 BIOS HD limitation question

Postby Jo22 » 2018-2-09 @ 16:48

Jed118 wrote:Blast... I suppose I could try to find a BIOS update...
Thanks for the read, it jogged my memory of these issues, which I haven't encountered in 10+ years ;)

You're welcome. :)

(Btw, in the article, L-CHS stands for Logical CHS (the fake drive geometry) and
P-CHS for Physical CHS (the real geometry; the parameters an old IDE or MFM/RLL hard disk actually used))

derSammler wrote:You can use Drive Overlay Software.

Yup, that's right. :) Ontrack and EZ-Drive are available at Phil's Computerlab, for example.
Here's a direct link to the Ontrack page: https://www.philscomputerlab.com/ontrac ... nager.html

For Windows 3.11, there's also the MicroHouse driver (I mentioned it in an older thread).
It does work with LBA and is compatible to the EZ-Drive overlay, I believe.

Anyway, it is not absolutely necesary for Windows. Just nice to have to
(I recall FastDisk drivers allowed DOS sessions in 3.11 to be windowed, etc.)

More about FastDisk can be read here :
http://stason.org/TULARC/pc/enhanced-ID ... _work.html
http://www.os2museum.com/wp/how-to-please-wdctrl/

Edit: There's also XT-IDE Universal BIOS. Currently, it supports up to 8GB, I believe.
As far as I know, there are three binary flavors right now. XT, AT and AT 386 (optimized or uses 32-Bit code ?)
Each of them comes in a full (with menu) or lite version. The small versions are neat if someone wants to save free space in the 640KB-1MB region.

Edit: Since the OP likes to use SCSi drives at some point..:
I recall there also was at least one Win 3.11 FastDisk driver for SCSI drives.
It was made by one of the big manufactureres (Adaptec, maybe ?)
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