This file format is compression format developed by Robert K. Jung. Its whole name is Archived by Robert Jung. Its main advantage is ability to part certain file into individual parts, because at an earlier time speed of internet connection was not very high. Then its second advantage was that it was able to work on 16bit, 32bit and even on 64bit operating systems in its time.
In half of 90s this format was one of two most used compession file formats. Second one was file type PKZIP, which was much more popular, but fame has come also to ARJ file format. That was due to its abilities. To this day there are versions for DOS – 2.86 and for Windows – 3.20.
There is one application that allows to open these files and it is from Robert Jung alone. This application is called File Archiver ARJ. Its latest version was released in 2001 and it was created for MS – DOS. To much more known application belongs 7 – Zip, which can edit and view it.