Software is different, and there was an exception in 2006 signed into the DMCA by the Library of Congress specifically for "abandonware."

2. Computer programs and video games distributed in formats that have become obsolete and that require the original media or hardware as a condition of access, when circumvention is accomplished for the purpose of preservation or archival reproduction of published digital works by a library or archive. A format shall be considered obsolete if the machine or system necessary to render perceptible a work stored in that format is no longer manufactured or is no longer reasonably available in the commercial marketplace.

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It is still illegal to distribute copyrighted software, even old software, but it is not illegal to make accessible an archive of preserved software; provided it meets the above requirements. Pretty much anything that was released on a CD does not qualify. CDs are both still manufactured and reasonably available in the commercial market.

As of 2010, however, Sonly officially retired the floppy disk and stopped all manufacturing. So basically any software sold on a 3.5 and 5.25 floppy disk (and only on a floppy disk) would be OK to archive. Everything else is vorboten. There may be some gray area between archiving the floppy disk version of software, but not the CD version.