SIO2HD FDD I could go for. But for HDD use, why opt for slow SIO speeds when there are fast HDD options such as MIO or MyIDE? And both of those can use modern, available HDDs, while ST-506 has been obsolete for decades, the drives are a pain to set-up, they're rare, old, as noisy as a dot-matrix printer, unreliable, and are going to cost you more than even an old IDE or SCSI-I drive.