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. Some of IBM’s software packages were also distributed on XDF diskettes. 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. This came at a time when CD-ROMs were not yet ubiquitous and software was distributed on rapidly growing piles of floppies. Since floppies were relatively expensive to manufacture and duplicate, shipping software on, say, 16 diskettes instead of 20 was an attractive proposition.
The XDF technology was not developed by IBM. The inventor was Roger D. Ivey (as can be seen in a XDF disk’s boot sector) and was first licensed to IBM by Backup Technologies, Inc. of Tampa, FL. Roger Ivey had previously written the Fastback PC backup software. Later releases of XDF software list Ametron Technologies, Inc. as the licensor. Ametron is a company specializing in selling intellectual property.
The XDF technology used several interesting techniques to achieve both higher storage capacity and speed. The XDF utilities mentioned “Patent(s) Pending” but there is no obvious record of a relevant patent ever being granted by the USPTO. Let’s take a look at some of XDF’s tricks. Continue reading
