Hi Jan, is there anything that can be done to help this motherboard? 😀

Sunlogix 80386-33/40 (Micro Express Computer) - Config Questions now

Chkcpu wrote on 2022-08-21, 19:17:

I’ve also put newly patched BIOSes for these boards on-line. As usual, these BIOSes have both K6plus and 128GB HDD support:
(...)
• PCChips M550

Does anybody know where to find that patched BIOS for the PCChips M550?
There's one on Jan's page but that one doesn't add compatibility for >8GB HDD support (albeit it adds K6-2 CXT support). And it's from 2006, so it wasn't "newly patched".
I also checked wims.rainbow-software and theretroweb to no avail.

tauro wrote on 2023-09-01, 08:10:

Does anybody know where to find that patched BIOS for the PCChips M550? There's one on Jan's page but that one doesn't add comp […]
Show full quote

Chkcpu wrote on 2022-08-21, 19:17:

I’ve also put newly patched BIOSes for these boards on-line. As usual, these BIOSes have both K6plus and 128GB HDD support:
(...)
• PCChips M550

Does anybody know where to find that patched BIOS for the PCChips M550?
There's one on Jan's page but that one doesn't add compatibility for >8GB HDD support (albeit it adds K6-2 CXT support). And it's from 2006, so it wasn't "newly patched".
I also checked wims.rainbow-software and theretroweb to no avail.

Hi tauro,

As you may have gathered, my main interest is the Award BIOS, although I did patch a few AMI socket 7 BIOSes as well.
But I never modified a BIOS to break the 8GB HDD barrier, Award, AMI, or otherwise.
As you probably know, this mod would involve adding the IBM/Microsoft Int 13h extensions to the Int 13h interface. As the BIOS Interrupt 13h handler is already a very complicated piece of code, I’m afraid such a mod is way beyond my expertise. 😉

However, most BIOSes from 1998 or later will support the Int 13h extensions and I have seen this > 8GB support in several BIOSes from the second half of 1997 as well.
So I checked the latest M550 Release 11/17/1997S BIOS and was pleasantly surprised to find Int 13h extensions support in this BIOS, therefore it should support drives up to 128GiB and so will my patch J.2 version of this BIOS.

But be aware that a lot of these 1997/1998 AMI BIOSes don’t Auto detect larger than 8GB drives correctly and only give you CHS values for 8064MB. Therefore you have to enter the CHS values manually via the ‘User’ Harddisk Type selection in the BIOS. These so called pseudo CHS values for these larger drives can easily be calculated from the total number of sectors on the drive.
Set the Heads count to 255 and Sector/track to 63 and calculated the Cylinders count by dividing the total sectors number by 63 and then again by 255. Round the result down to a whole number and you have your Cylinders count.
Example: A 40GB drive has 82,092,176 sectors (of 512 bytes each). When you divide this value by 63 and the result again by 255, you get 5110.0016. So use CHS 5110/255/63 for this drive.
When you enter these values in your BIOS, you should see this:

And at the end of POST, you will see the same CHS and drive size in MB. I used the Secondary Master drive settings for this example.

This should work for drives up to 128GiB, but note that the drive size on the second POST screen is limited 65535MB. It will display this value for any drive larger than 64GiB, but the entered CHS values will be correct.

I hope this helps and I’m very curious if you can use a >8GB drive now with the 11/17/1997S BIOS.
However, when this manual CHS trick doesn’t work, we have the XTIDE Universal BIOS now which can be used to break the 8GB barrier, and this is what I’m using on my systems with a 1997 or earlier BIOS.
That said, when you do have an 8GB or smaller drive, that storage space is usually more than enough for these retro machines. DOS 5/6 and Windows 3.x don’t support more than 8GB drives anyway, but OSes like Windows 9x/DOS 7.x and NT4 with SP4 do.

Cheers, Jan

Chkcpu wrote on 2023-09-03, 17:29:

As you may have gathered, my main interest is the Award BIOS, although I did patch a few AMI socket 7 BIOSes as well.
But I never modified a BIOS to break the 8GB HDD barrier, Award, AMI, or otherwise.
As you probably know, this mod would involve adding the IBM/Microsoft Int 13h extensions to the Int 13h interface. As the BIOS Interrupt 13h handler is already a very complicated piece of code, I’m afraid such a mod is way beyond my expertise. 😉

I've read your guides, I'm very impressed. It's a bit too much for me at the moment to manually edit a BIOS file with a hex editor but I still can admire your work. I have done some small modifications with the BIOS editors such as unhide options. I know your main focus is Award, but since you posted about an M550 BIOS with support for 128GB disks, I had to ask, it seems like I misunderstood.

Chkcpu wrote on 2023-09-03, 17:29:

However, most BIOSes from 1998 or later will support the Int 13h extensions and I have seen this > 8GB support in several BIOSes from the second half of 1997 as well.
So I checked the latest M550 Release 11/17/1997S BIOS and was pleasantly surprised to find Int 13h extensions support in this BIOS, therefore it should support drives up to 128GiB and so will my patch J.2 version of this BIOS.

I could confirm that the IBM/Microsoft Int 13 extensions are installed in this BIOS, I used your tool for this.
So this is indeed great news!

Chkcpu wrote on 2023-09-03, 17:29:

But be aware that a lot of these 1997/1998 AMI BIOSes don’t Auto detect larger than 8GB drives correctly and only give you CHS v […]
Show full quote

But be aware that a lot of these 1997/1998 AMI BIOSes don’t Auto detect larger than 8GB drives correctly and only give you CHS values for 8064MB. Therefore you have to enter the CHS values manually via the ‘User’ Harddisk Type selection in the BIOS. These so called pseudo CHS values for these larger drives can easily be calculated from the total number of sectors on the drive.
Set the Heads count to 255 and Sector/track to 63 and calculated the Cylinders count by dividing the total sectors number by 63 and then again by 255. Round the result down to a whole number and you have your Cylinders count.
Example: A 40GB drive has 82,092,176 sectors (of 512 bytes each). When you divide this value by 63 and the result again by 255, you get 5110.0016. So use CHS 5110/255/63 for this drive.
When you enter these values in your BIOS, you should see this:
M550-40GB-1.png

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M550-40GB-1.png
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AMI BIOS manual drive setup

And at the end of POST, you will see the same CHS and drive size in MB. I used the Secondary Master drive settings for this example.
M550-40GB-2.png

Filename
M550-40GB-2.png
File size
71.13 KiB
Views
38 views
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AMI BIOS drive summary

That's a crucial bit info that I couldn't have guessed.

Once I "bricked" a 16GB CF card with a motherboard that only supported 8GB disks. I don't know how it happened. Maybe it's because I formatted the card inside Win98, which detected it's real size (16GB) but the BIOS didn't... and something went awry. It became so corrupted that there's no way to bring it back to life. It can only be formatted for 32MB now, but it's not really working. I'm not sure what really happened to it but it has left an impression on me.

So first I tried a 32GB card, with 61078752 sectors (as reported by fdisk on GNU/Linux), so 3801 CYL. Everything seemed right at first, albeit a little slow, but after two reboots or so, I started to get corrupted files, "Windows has detected a registry/configuration error.", and the filesystem then was irrecoverable. I used a 66MHz BUS and everything was within spec.
I installed Windows 98 SE three times on CF card and it was always the same corruption. So I gave up. I don't know if the card has a problem, but it has been working fine so, I presume there's some sort of incompatibility. Maybe 32 GB is too much for this BIOS?

Later I tried a 16GB card, with 31260096 sectors, so 1945 CYL.
This time things went flawlessly. It's working really well! 👏 😀

262.5MHz MMX (75MHz bus), DMA enabled

Chkcpu wrote on 2023-09-03, 17:29:

I hope this helps and I’m very curious if you can use a >8GB drive now with the 11/17/1997S BIOS.

It really did help 😀 I wouldn't have tried the 16GB card were it not for your guidance. I was planning to use a 4GB CF card and a PCI SATA controller and then load ISOs from there.

Chkcpu wrote on 2023-09-03, 17:29:

However, when this manual CHS trick doesn’t work, we have the XTIDE Universal BIOS now which can be used to break the 8GB barrier, and this is what I’m using on my systems with a 1997 or earlier BIOS.

It is indeed a great alternative, especially on older systems ≤486. The problem with it is that it slows down the performance on faster systems.

I'm planning to use this machine with an P55C and 64 MB of ram for 1980's and early to mid 1990's stuff. I already cleaned and retrobrighted a Baby AT case 👶. I'm going to wire the turbo button to change the bus speed, or the multiplier, I'm not sure yet.

I also recapped this board and replaced the Super I/O Chip because the floppy was not working. And gladly, that fixed it!

The only remaining obstacle is that the on-board USB is not functional. I've read this a known problem with this board. I'm using a v5.6 and it supposedly should work.
I tried all the BIOS I could find for it but it's the same with all.

Windows detects the USB controller, but it doesn't work. Plugging a mouse for example results in a brief red flash of the LED and then it immediately goes out. No device is detected by the system.

Disabling the USB controller on the BIOS menu makes no difference, Windows still detects it so... there's seems to be something wrong with the BIOS implementation.

Is there a chance that you could look that part of the BIOS? Or maybe this is a hardware limitation? I've made sure that I'm using the correct pins in the USB header. I tried inverting the data lines too in case they were flipped, but it didn't work. VCC is 4.9v. Do you have any advice on that? Is there something that I could try on the BIOS menu? What do you think that could be the reason it doesn't work?

Thank you very much again for your help, time and dedication, and shedding light on all these matters. 💡 💻

This is an awesome guide and very interesting. Been messing around with MODBIN and a hex editor..

Think you could help me with my modification of an 85C471 board here? Attempting to add larger RAM support to a 486 board

I wish to set chipset register 50, bit 2, to 1, during RAM initialization, to configure an unused multipurpose pin as MA11 needed for large SIMMs.
The BIOS may also have a hard 64MiB limit elsewhere. Not sure...
There are many other 85C471 BIOSes out there that claim to support 128MiB RAM (the chipset maximum). I believe this would only be possible with MA11 working.

Jan, when do we get the next episode? :p

nztdm wrote on 2024-02-19, 21:48:

This is an awesome guide and very interesting. Been messing around with MODBIN and a hex editor.. […]
Show full quote

This is an awesome guide and very interesting. Been messing around with MODBIN and a hex editor..

Think you could help me with my modification of an 85C471 board here? Attempting to add larger RAM support to a 486 board

I wish to set chipset register 50, bit 2, to 1, during RAM initialization, to configure an unused multipurpose pin as MA11 needed for large SIMMs.
The BIOS may also have a hard 64MiB limit elsewhere. Not sure...
There are many other 85C471 BIOSes out there that claim to support 128MiB RAM (the chipset maximum). I believe this would only be possible with MA11 working.

Hi nztdm,

Yes, I saw your Attempting to add larger RAM support to a 486 board thread and read it with interest.

However, I never had the need to expand RAM support on socket 3/5/7 boards so my knowledge on patching a BIOS for that is very limited.
Although my SiS471 board (Chicony CH-471B Rev 1.0) has four 72-pin SIMM slots and supports 128MB RAM when using double sided SIMMs in all 4 slots, I never had more than 32MB RAM on this board. With an Am5x86-133 CPU and 256KB L2 cache, both in WB mode, this system runs Win95 just fine. 😉

When I find more info on this BIOS/RAM issue, I’ll report in your thread.

Greetings, Jan

Sphere478 wrote on 2024-02-20, 00:51:

Jan, when do we get the next episode? :p

Hi Sphere478,

Yes, the plan to continue with this BIOS modding guide keeps being derailed by life events. 😉

But I have now notes on paper about what I want to tell in the coming 2 episodes. There I will explain in detail how to handle the compressed Award BIOS when applying a patch. This part of the guide has to be very clear, otherwise you end-up with a corrupted BIOS and a bricked board. 😉

When this hurdle is taken, I can continue with the story on what you can do to get K6plus and > 32GB HDD support.

Cheers, Jan