Early on the the PC world many modems had db-25 as the serial connector.
I think IBM pc-xt's actually used some of the extra pins for some type of talk-back/ACK for synchronous modems.
While the db -25 cables and gender changers are usualy just pass through and can be used for either serial or parallel use. This adaptor will NOT convert serial to parallel.
Dig this for more info http://www.jspayne.com/io/schematics.html
JHV