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Is there a UDF filesystem driver for DOS? (Users)

posted by bretjohn Homepage E-mail, Rio Rancho, NM, 20.05.2013, 18:14

> We have ExFAT, FAT32, and even NTFS support in DOS, but I can't find a
> driver which allows the UDF filesystem to be read. Is there one released,
> buried somewhere in obscurity? Or a UDF bootloader?
I wouldn't exactly call what we have for ExFAT now to be "support" -- it requires ASPI, which is only available with some USB drivers. You couldn't put ExFAT on a "regular" (INT 13h) disk today and have it work properly.

AFAIK, there is no UDF driver for DOS. I wish there was one. It would come in real handy for some of the upgrades I'm working on in the USB drivers.

Just as an FYI, there are currently five different versions of UDF that should be supported: 1.02, 1.50, 2.01, 2.50 and 2.60. It would also be nice to have Joliet support for CD's (which I don't think exists today, either).

> Does any version of DOS natively support > 512 byte sector size? I can't
> seem to locate any version which does.
Depends on how you define "natively". MS-DOS will support sector sizes up to 8k, and probably up to 32k (not 100% sure about 32k), but "turning on the support" is troublesome.

Through some experimentation by Czerno, it appears that up through version 6, MS-DOS will do it automatically if the kernel finds a disk with sector size > 512 bytes while it is booting (this happens even before CONFIG.SYS is processed). In MS-DOS 7+, it appears to do it if either the kernel finds a disk with sector size > 512 bytes while booting, or if a block driver in CONFIG.SYS (like a driver for a RAM Disk) is installed with sector size > 512 bytes. AFAIK, though, there are no RAM Disk drivers that use anything other than 512 byte sectors.

You can also modify the kernel (MSDOS.SYS) as described in the notes for USBDRIVE.A36 (the source code for my USBDRIVE program), starting around line 289. All you need to do is change one word of in the MS-DOS kernel to change the maximum sector size it will support, and you won't necessarily need to install a special hard drive or create a special RAM Disk driver.

However, this is only true for MS-DOS. It is probably also at least partially true for PC-DOS, since MS-DOS and PC-DOS have an "overlapping" history. I know FreeDOS does not currently support anything other than 512 byte sectors, and I don't think any of the FreeDOS utilities do either (FDISK, FORMAT, caching programs, etc.). I don't know about any of the other DOS versions (like DR/Novell/Caldera).

This is actually a big problem, since disks with 4k sectors (disks larger than 2 TB) have been around for a while now.

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