This item is from the Yet Another Enhanced IDE/Fast-ATA/ATA-2 FAQ, by John Wehman and Peter den Haan with numerous contributions by others. (v1.92).
This is a convenient option, but there are caveats.
The software, sometimes bearing an exotic name depending on the licensee, is usually a version of either MicroHouse's EZ-Drive or OnTrack's Disk Manager. Disk Manager, when used on the boot drive, has to resort to some trickery in order to be loaded very early during the boot process (which is necessary for technical reasons). This is accomplished by modifying the Master Boot Record (MBR), the first piece of code the BIOS loads and executes when the computer boots, and storing a Dynamic Drive Overlay (DDO) on the very first disk track. EZ-Drive works in a similar fashion.
An annoying side effect of using a software solution is that operating system installations, which often overwrite the MBR, will render the contents of your harddisk inaccessible. You will need to restore the MBR from the installation floppy to regain access to your partitions.
Moreover, such software tends to create partitions quite different from 'standard' translation schemes as used by most Enhanced BIOSes. Many device drivers dealing with the disk will fail even if they work fine with other schemes. Important examples are (E)IDE interface drivers; remember that without these drivers an interface will in general be much slower. You'll need drivers that are specifically aware of the translation software you use. Also, many operating systems other than DOS will not be able to access or use the drive, at least not 'out of the box'. Disk fixing utilities may fail to work if the partition table or the overlay is damaged.
This also makes it difficult to upgrade to a BIOS based solution. OnTrack Disk Manager version 7 includes a migration utility for the purpose and improves on version 6 in a number of other ways. It allows multiple operating systems and is compatible with most interfaces and drivers, including those for ATAPI CD-ROMs. Owners of version 6.03, which is still often included with hard drives, can download an update patch from OnTrack <http://www.ontrack.com/pub/software/dmpatch.zip> that gives some of the benefits of version 7. View <http://www.ontrack.com/dm.html> for general information.
For older versions of Disk Manager, IBM and Microsoft have fixes for OS/2 (in FixPak 5 or later, or out of the box in Warp FullPack and Warp Connect) and NT (Service Pack 2). Win95 should support Disk Manager and EZDrive out of the box (see Microsoft KnowledgeBase article Q126855, "Windows 95 Support for Large IDE Hard Disks"). More about Disk Manager in section 13.1.