Hunk is the executable file format of tools and programs of the Amiga Operating System based on Motorola 68000 CPU and other processors of the same family.
[1] This kind of executable got its name from the fact that the software programmed on Amiga is divided in its internal structure into many pieces called hunks, in which every portion could contain either code or data.
Their structure was officially codified and could be changed only by a Commodore committee, which then communicated the modifications to the developers for new releases of the Amiga operating system.
These are all valid names for programs or tools, because AmigaOS does not differentiate between filename extensions.
The Amiga saves some metadata into sidecar files known as ".info" (so called from the name of their extension suffix).
When the user clicks on the icon with left mouse button, the project ".info" calls the program which originated it.
By invoking arguments such as "Screen=800x600" and "Depth=8" into the info file dialog box, the user can save this information into the associated ".info" file and then program would open the productivity software into its own screen sized 800×600 with 8 bits of colour depth (equal to 256 colors).
The users can deal with icons by using the AmigaOS standard program "IconEdit", present in the operating system since its early versions.
Third-party icon "engines" exist, which try to keep the look of AmigaOS up to date with modern standards of other Operating Systems.
These programs patch the OS routines dedicated to icon handling, replacing them with custom ones.
The HUNK_OVERLAY type was intended to reduce the amount of RAM needed to run a program.
Executables with an overlay structure have a root node which is in memory at all times, and the rest of the program is split into smaller modules which are loaded and unloaded automatically when needed.
With third party add-ons AmigaOS up to 3.9 recognizes various kinds of executable files other than Hunk format created for Motorola 68000.
[5] In 1997 Haage & Partner developer WarpUp PowerPC kernel for PowerUP accelerator boards.
Extended Hunk Format (EHF), developed by Haage & Partner, allowed mixing PPC and 68k code to single executable without modifying the existing system if PowerPC accelerator was not installed.