| Filename extension |  .SHK (regular NuFX archives), .SDK (NuFX disk images) | 
|---|---|
| Initial release | 1987? | 
| Latest release | 1.0.6 (GS), 3.4 (Apple II) GS: 30 April 1992, A2: 24 January 1991 | 
| Type of format | Data compression | 
| Extended from | .BNY (Binary II envelope) .BQY (squeezed file in Binary II envelope) .BXY (NuFX in Binary II envelope) | 
| Extended to | .SDK NuFX disk image | 
A NuFX archive is an archive file format that supports lossless data compression. It is usually given the file extension SHK; SDK may also be used to specify that the archive describes the entire contents of a disk.
Andy E. Nicholas designed the format as an improved replacement for the Binary II (.BNY) format, adding compression. He introduced it alongside a pkzip-like program called ShrinkIt for Apple II systems, which he later migrated to the Apple IIGS as GS-Shrinkit.
The specification was republished by Apple in its File Type Notes. [1]