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Partitioning of 4TB HDD for legacy OSes (Users)

posted by bretjohn Homepage E-mail, Rio Rancho, NM, 29.04.2026, 03:39
(edited by bretjohn on 29.04.2026, 04:21)

> bret, when you say your USB utilities enable GPT partition reading in DOS,
> this is only for USB devices, correct? You do not patch DOS to enable GPT
> reading of all non-bootable partitions attached to the system (including
> SATA / AHCI internal drives?)
That is correct. The USB driver add entries in the various DOS internal tables that keep track of drive letters and such, responds to INT 13h requests (including the 64-bit extensions), and inserts block device drivers into the device driver chain. It does not modify anything about DOS itself -- just creates new entries in the appropriate places.

In addition, since somebody brought it up, the USB driver will work with sector sizes other than 512 bytes if the DOS supports it (which MS-DOS does if you set it up correctly but AFAIK none of the others DOS's do). Unfortunately with DOS, you need to add support for non-512-byte sectors not just to the kernel but also to ALL of the disk-related utilities (and there are a BUNCH of those). And even though the MS-DOS kernel supports sector sizes other than 512 bytes, I don't think any of the MS utilities do (though a few might).

I'm also adding support for CD/DVD/BD to the USB driver, but still have some more work to do. What I have got to work (that I think is pretty cool) is accessing a DVD-RAM disk, which (like all common optical media) has a 2k sector size, formatted with FAT32. I can mount this in MS-DOS as a regular drive letter and MS-DOS treats it as a FAT32 hard drive with 2k sectors and doesn't know it's a DVD-RAM. I used Windows to format the DVD-RAM since there aren't any DOS utilities that will do it (and it's possible that newer versions of Windows won't do it either). Unlike most read-write optical media which have a pretty limited number of writes, a DVD-RAM is actually designed to be written to many times -- it's sort of like a really big floppy drive. Unfortunately, nobody seems to make new DVD-RAM media any more and it's really hard to find.

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