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Stupid question about BIOS extensions

Thallanor

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Joined
Sep 16, 2018
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27
As the title implies, I have a dumb question about BIOS extensions. I know that some can bring new functionality to some PCs, but I was wondering what the limits of this are? For example, I have a PC with a floppy controller that supports double density drives. I do have an ISA card with a floppy controller that supports high density, but because the FDC cannot be disabled on this PC, installing the card doesn't work due to that conflict. Here is where my question comes in: is it possible to add support for HD drives through a BIOS extension, like if I used one of my ISA NICs and flash something? Or is this 100% totally on the FDC and if it doesn't support it, it just doesn't support it?

Just wanted to run it past you guys and hear from people far smarter than myself. :)
 

SomeGuy

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Yes. If you search the forum you will find various threads about adding high-density floppy BIOSes in such a way to use BIOS-less 16-bit AT controllers stuffed in an XT 8-bit slot.

However, such BIOSes will not resolve your I/O port or other hardware conflicts.

Additionally, if you use a floppy controller set to use different addresses, then software that bypasses the BIOS will still not function unless it specifically supports a secondary controller.
 

Xacalite

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Typical XT FDC only support double density (and probably single density, but that's irrelevant for PC disks).
For high density support, you definitely need to install high density hardware. A BIOS extension is not enough.

If you can't disable the onboard FDC, you need an FDC that can be set to secondary address, and the BIOS extension must support it on the secondary address.
I think some GSI FDC card claimed to support such a setup.
 

Thallanor

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Sep 16, 2018
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Typical XT FDC only support double density (and probably single density, but that's irrelevant for PC disks).
For high density support, you definitely need to install high density hardware. A BIOS extension is not enough.

If you can't disable the onboard FDC, you need an FDC that can be set to secondary address, and the BIOS extension must support it on the secondary address.
I think some GSI FDC card claimed to support such a setup.
Thank you. I'll need to take a peek and see if I can dig up such a beast. I have SCSI now, but I want to use one of these USB drive emulators. I did find something similar for SCSI, but for several hundred dollars. Ugh.

All of this stems from my Tandy 1000 TL/2 having an option in the BIOS to disable the FDC but it does nothing. There is a utility someone created that disables it on boot (so you couldn't boot from it) but it just locks up my Tandy badly. D'oh.

Thanks again for the advice. :)
 

Plasma

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Nov 7, 2005
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You could get an external parallel port 3.5" floppy drive and replace the drive with your USB emulator.
 

Plasma

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Well it's only a "big problem" if OP needs to boot from it...
 
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