Wikipedia
WHDLoad is a software package for the Amiga platform to make installation of software to a hard disk easier, for such things as demos or games. Allowing for better compatibility for Amiga software, which can sometimes have hardware incompatibilities making them hard to use in emulated environments due to the widely varying hardware specifications of the Amiga product line across its history. WHDLoad basically circumvents the operating system in the Amiga for greater compatibility and preserves the original program environment.
WHDLoad makes it possible to autostart an installed floppy disk image by clicking an icon.
Two special parts are required, each one especially written for the client program: To install media, it must be read from the original disk and written to an image file on the hard drive by the "Imager". Then the installed program can be run from a virtual disk drive with the "Slave" interface.