With 3½” HD floppies, it is possible to use more than the standard 18 sectors per track the hard limit appears to be 21 sectors which translates to 1,680KB total with 80 tracks. The basic problem with higher density floppies when using 512-byte sectors is that once more than 10 or so sectors per track are used, significant capacity is lost to inter-sector gaps, address marks, CRCs, an other “useless” overhead. Let’s take a look at some of XDF’s tricks. The XDF utilities mentioned “Patent(s) Pending” but there is no obvious record of a relevant patent ever being granted by the USPTO.

The XDF technology used several interesting techniques to achieve both higher storage capacity and speed. Ametron is a company specializing in selling intellectual property. Later releases of XDF software list Ametron Technologies, Inc. Roger Ivey had previously written the Fastback PC backup software. Ivey (as can be seen in a XDF disk’s boot sector) and was first licensed to IBM by Backup Technologies, Inc.

The XDF technology was not developed by IBM. Since floppies were relatively expensive to manufacture and duplicate, shipping software on, say, 16 diskettes instead of 20 was an attractive proposition. This came at a time when CD-ROMs were not yet ubiquitous and software was distributed on rapidly growing piles of floppies. XDF allowed the user to format a 3½” floppy which normally holds 1,440KB of data to a special format with 1,840KB capacity (well, almost-see below), or almost 28% improvement. Some of IBM’s software packages were also distributed on XDF diskettes. In 1994, IBM started shipping software with support for XDF, or eXtended Density Format, first in OS/2 Warp and a few months later in PC DOS 7.0.

Ibm formatted floppy disks