CoffeeOne wrote on 2023-05-07, 18:46:

Hi Jan, may I ask an off-topic question. You patched a lot of BIOSes, so I would like to know the following: […]
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Hi Jan, may I ask an off-topic question.
You patched a lot of BIOSes, so I would like to know the following:

Many "modern" 486 BIOS have LBA support, but they do have a 7.8GB Bios limit (something a bit below 8GB I believe).
I am talking of the Asus VL/I-486SV2GX4 and the Asus PVI-486SP3, I have those 2.
Would it be possible to overcome the 8GB limit with a modified Bios?

Hi CoffeeOne,

I agree the “modern” socket 3 and early socket 5/7 BIOSes would be a good candidate for such a patch, provided there is enough unused space in the ROM to add the code.

Alas, I never modified a BIOS to break the 8GB HDD barrier.
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. 😉

As < 8GB mechanical drives are unobtanium these days, and many people are using CF or SD cards now with the smallest new-bought sizes being 16 GB or larger, this is a real problem for pre-1998 machines.
Luckily 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

aaronkatrini wrote on 2023-05-06, 13:17:

Hi,

Eprom was not the issue, I already tested the board with the new BIOS. A correctly flashed Eprom was provided by a friend of mine.
He also provided me with already erased other Eproms for future use 😀

Hey, a couple of suggestions:

1st: I double for a germicidal lamp. In my area you can get one of those (see the picture below) used for like a 1/5 of a price for a used eraser, and it usually takes 6-20 minutes for full erase depending on particular IC and you can heal your nose and lip infections when needed as a bonus 😀

Erase by the sunlight can take about 5 days averagely but this depends a lot on the real exposure term, the angle, ozone holes, etc. the needed wavelenght (up to 400nm) is very stiff band which fortunately to life on Earth, is mostly absorbed by the skies, so it is weak and will take several days any way. If you’re able to put the chip on a roof for a week, go for it but I’d rather get a UV lamp. And yes, blacklight doesn’t work, it’s very weak in the needed wavelength range.

As for the 4x multiplier, I was able to run 5x86 CPU on the same MB by connecting one pin of J25 to the GND with a dupont wire and putting resistors array to positions RP12 and RP14.

The positions of J14 and J21 don’t matter in my case.

The modified BIOS is awesome!