LBA 48bit vs 28bit BIOS support and DOS/Windows 98 FAT32 limits

Vintage Computing

As you know for sure, LBA (logical block addressing) comes in two flavors, the early 28bit LBA implementation and the later LBA 48bit.
LBA is not implemented for early PCs (but approx. since Intel 80386 CPU PCs raised), and unfortunately also later sold PCs have often only 28bit BIOS support.
This is also mentioned on several web sites in relation with DOS 7.1 aka Windows 95B, Windows 98,SE (ME has a higher DOS number, but is not used standalone).

MS-DOS until Version 7.1 does not support FAT32, which theoretically supports up to 268.435.456 cluster – a cluster is usually a sector; before 4K block drives appeared, a harddisk sector had only 512 Bytes. That means you can use drives up to 2 TeraBytes.

Practically you will reach a lower limit often, 137GB. This limit is NOT related with FAT32, but with Microsoft tools like FDISK and FORMAT (in DOS 7.1) or with the build-in Formatting Routine in modern Windows implementations.

DR-DOS 7.03 with DRFAT32.SYS driver does support also FAT32, and so some unofficial published and modified versions of DR-DOS 7 (e.g. DR-DOS 7.01.06). Unfortunately DR-DOS has still a 2GB limit for the first partition. But give FreeDOS also a try, this will work for sure.

If you want to use larger harddisk drives with DOS 7.1 (at least larger than 64GB), you need a corrected version of FDISK. You will not find the file anymore on Microsoft pages, but to the rescue, has still them.

To visit the original Microsoft page (archived with the last time in 2018, there is NO info about this problem anymore online), click >here< (or search for „263044usa8.exe“ for an english, or „263044ger8.exe“ for a german version of the patch).

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