System 5

System 5, strictly speaking, was a non-existant version of the Mac OS.

Closely related to "System 5" is System Software 5.0, which included System 4.2, Finder version 6.0, MultiFinder 1.0 and LaserWriter version 5.0.

No version of the System file was ever numbered "version 5".

Refer to

 * System 4.2

Sources and References

 * The Mac 512: System version numbering scheme