SDN (SDN Project)

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File Format
Name SDN (SDN Project)
Extension(s) .sdn, .sda
Released 1989

An .SDN file is a compressed archive file associated with the SDN Project organization, and the SDNet/Works! software distribution network. SDN stands for Shareware Distribution Network. SDN files are cryptographically authenticated.

An SDN file might be accompanied by an .SDA "abstract" file, which is apparently just a text file describing the software in the SDN file.



There are at least two or three different SDN formats.

The documentation for the SDNV utility says:

SDN FILES BEFORE JUNE 15TH 1990.........................................
Files with  a .SDN extension  that were  packaged before June  15th 1990
were compressed using NoGate Consulting's PAK v2.10 utility. [...]

SDN FILES AFTER JUNE 15TH 1990..........................................
All files and programs, released  for distribution on SDNet/Works! after
June 15th  1990 will be  secured and  compressed in SDNV  format.  Other
archivers will not be able to read  or uncompress these .SDN files.  You
must use a the  SDNV utility SDNV.EXE. [...]

The older format is a PAK file with a special extended record. PAK itself is a variant of ARC.

More research is needed, but it seems possible that the plan to switch to SDNV format was abandoned.

In 1993, it was announced[1] that SDN files would switch to a format based on ARJ.

ARJ v2.41 (early 1993) introduced "SDN support". We've seen some ARJ files that use the SDN "security envelope" feature, but they have a .ARJ file extension, not .SDN. It's unclear if the .SDN file extension was ever routinely used for the SDN-ARJ format, though the ARJ documentation suggests that it was.


PAK format:

SDNV format:

ARJ format:

Sample files

PAK format:

ARJ format:


  1. fido1004.txt - "SDN Changing Compression and Security"
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