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Adding large disk support to INT13h (Users)

posted by mceric, Germany, 01.04.2024, 22:25

> my Pentium MMX motherboard INT13h functions do not support disk sizes
> larger than 8.4GB, but the chipset does. Is there any open source solution
> to add large disk support that does not require me putting in another
> controller or burning an XT-IDE rom?
I think you want an open source alternative to ontrack or ezdrive? You could start with XT-IDE and write a little loader to put it in RAM. The closed source tools mentioned are similar, they come with a MBR to load them in RAM, often allocated via manipulation of 40:13 memory size.

They typically even hide themselves by shifting the entire disk contents, so the initial part where the "driver" resides is only visible until the "driver" gets loaded. As there usually is plenty of space in the first track, I disliked that method. If you write some open source xt-ide loader, avoid such shift tricks if possible. You could even load it "metakern style" from a DOS boot sector and then chain load the normal DOS kernel after the "driver".

Note that most older IDE controllers are not smart, so they have no opinion about CHS versus LBA. Only the different PIO, DMA and UDMA styles available are likely to actually depend on your hardware.

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