For reference, I have the Octek Hippo 15 and an A-Trend ATC-1425B motherboard that I would love to unlock the limit on.

You need a different HD controller

The solution I wish existed back in ye olde times was instead of a jumper limiting the hd in size to 32gb or 128gb why not instead split the drive so it appears as 2 drives to the controller? That would have not been much more complex than limiting capacity, also worth noting I have encountered IDE cables with more than 2 connectors with NON-Hardrives plugged in the 3rd slot, unfortunate such solutions weren’t standard.

rmay635703 wrote on 2025-11-19, 18:20:

You need a different HD controller

Does this also hold for the 8.4GB limit?

eton975 wrote on 2025-11-19, 18:23:

rmay635703 wrote on 2025-11-19, 18:20:

You need a different HD controller

Does this also hold for the 8.4GB limit?

Nope 128gb is the real hardware driven limit but it was rather complex going past the 8.4gb limit (as compared to the 32 or 40gb limits) because the bios cores fundamentally changed.

Obviously not impossible but you need to re-write the bios or switch to a different brand bios for the same or similar board.

The resident expert on adding large disk support

DIY Bios Modding guide Jan Steunebrink k6-2+/3+ 128gb

I don't see how there would be a hardware limitation. 48-bit LBA accesses can still be done using Programmed I/O (https://wiki.osdev.org/ATA_PIO_Mode#48_bit_PIO)
ISA IDE interfaces should just be dumb logic that pass port i/o between the ISA bus and the ribbon cable. As long as the drive (and more importantly, OS) supports it, it should work.
XT-IDE Universal BIOS or another overlay BIOS is a much easier solution.
For comparison, someone had a question about whether you could retrofit 8.4GB LBA support into an old AMIBIOS, and here were two "color" BIOSes where that is the only difference: Re: AMI Color BIOS (1993 and earlier) modification in hex editor

The MBR disk layout will still exhaust, unless you play silly games with the sector size.

32 bit sector fields and 512 byte sectors (2^9) is 2TB for MBR format. The idea of a 128GB MBR format limitation is an AI hallucination

2tb can be reached with very very new drives. 😁
(A 4tb sata ssd is about 150$ from newegg, for instance)

Why anyone would want to put one on a dos machine escapes me.... maybe they want to multiboot with XP, where NTFS can in theory work with a volume that large? Dunno. Not going there.

Just that the full size allowed by lba48 will exhaust the allowable mbr size, unless you do silly stuff.

Hi eton975,

I second jakethompson1’s reply that XT-IDE Universal BIOS or another overlay BIOS is the easiest solution here.

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.

And then there is the BIOS space constraint. These 486 BIOSes are mostly 64KB and have a 1995 or earlier date. 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, but these were all 128KB in size.

I found that when you do have an 8GB or smaller drive, that storage space is usually more than enough for these 486 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.
But when I do need more storage space on a late 486 or early Pentium system with a 1997 or earlier BIOS, the XTIDE Universal BIOS is my solution of choice.

Cheers, Jan

Chkcpu wrote on 2025-11-21, 10:55:

Hi eton975, […]
Show full quote

Hi eton975,

I second jakethompson1’s reply that XT-IDE Universal BIOS or another overlay BIOS is the easiest solution here.

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.

And then there is the BIOS space constraint. These 486 BIOSes are mostly 64KB and have a 1995 or earlier date. 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, but these were all 128KB in size.

I found that when you do have an 8GB or smaller drive, that storage space is usually more than enough for these 486 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.
But when I do need more storage space on a late 486 or early Pentium system with a 1997 or earlier BIOS, the XTIDE Universal BIOS is my solution of choice.

Cheers, Jan

Hi Jan,

By overlays do you also mean dynamic drive overlays like OnTrack Disk Manager and the like? I will keep such in mind

BTW, no offense meant: you are not quite correct about the BIOS size on some later 486 boards, those are typically 1Mbit/128KB in my experience. I'm not saying this makes it easy to mod such interrupt 13h extensions in though.

Ah, saw that you addressed that statement, whoops.

I avoid ontrack becuase the early versions make proprietary partition types that often come back to sting you if you take the drive to a different computer or boot from floppy. The later versions are better behaved and can get you past the lba 28 limit, but they tend to be a little heavier to install, 2 disks, 16 mb ram. I prefer easydrive 9.09. One disk. Reasonably well behaved. Or xtide bios if you have an old nic with a spot for an option rom.

Easiest is to add XT-IDE Universal BIOS on an ISA card, or embed it in the existing BIOS (contingent on having enough empty space). Disassembling and rewriting parts of the BIOS would be a lot more effort.

The other question is what OS you are going to run, and what size disks it can support. No point trying to install a 250GB IDE to run DOS.

bakemono wrote on 2025-11-23, 17:07:

Easiest is to add XT-IDE Universal BIOS on an ISA card, or embed it in the existing BIOS (contingent on having enough empty space). Disassembling and rewriting parts of the BIOS would be a lot more effort.

The other question is what OS you are going to run, and what size disks it can support. No point trying to install a 250GB IDE to run DOS.

Sometimes you need to dance with who you came.

At this point anything under 1tb can be an antique if it’s ide compatible.

Being able to use a drive, even if you can only access 8.6gb of it may be useful so long as the drive stays readable in a modern machine.

Reason being a functional 80gb ide drive is quite likely cheaper than an 80mb one at this point.

eton975 wrote on 2025-11-19, 18:02:

A-Trend ATC-1425B

My experience with two different revisions of Lucky Star LS-486E boards is that trying to load XTIDE will hang the system - I don't believe the built-in HDD controller for SiS496/497 will allow itself to be taken over by XTIDE. Your best bet is to use a PCI Promise HDD controller, but that has the downside in that you can't set up a portable Win9x system. FreeDOS, MS-DOS and Win3.11 are perfectly fine for swapping between systems, even if MS-DOS does practically limit you to 8GB in total partition size.

PCI Promise IDE controller. Not only do you get support for large drives but also the speeds are much better then onboard IDE of any 486

DEAT wrote on 2025-11-24, 21:49:

eton975 wrote on 2025-11-19, 18:02:

A-Trend ATC-1425B

My experience with two different revisions of Lucky Star LS-486E boards is that trying to load XTIDE will hang the system - I don't believe the built-in HDD controller for SiS496/497 will allow itself to be taken over by XTIDE. Your best bet is to use a PCI Promise HDD controller, but that has the downside in that you can't set up a portable Win9x system. FreeDOS, MS-DOS and Win3.11 are perfectly fine for swapping between systems, even if MS-DOS does practically limit you to 8GB in total partition size.

Will an Ultra100 PCI work, or will it need to be an Ultra66 due to the age of the system?

eton975 wrote on 2025-11-25, 05:11:

Will an Ultra100 PCI work, or will it need to be an Ultra66 due to the age of the system?

Either should work fine, but both are likely limited to drives <128GB, if that matters.

douglar wrote on 2025-11-25, 10:41:

eton975 wrote on 2025-11-25, 05:11:

Will an Ultra100 PCI work, or will it need to be an Ultra66 due to the age of the system?

Either should work fine, but both are likely limited to drives <128GB, if that matters.

I guess it depends on what happens if you attach an lba 48 drive
my older PCCHIPS socket A board with a 160gb drive ended up only able to use like 32gb if I didn’t upgrade and just used it native.

Everything seemed to work despite using the drive in a kitty whumpus way.

If you don’t care about how much of the drive is usuable…
Only issue is that data on the drive will likely only be usuable on the pc creating it.