Magnetooptical disks and drives
Magnetooptical drives used magnetic and thermodynamic
properties to efficiently store data (see FAQ). It was not commonly used,
as it wasn't cheap. MO drives, in 3.5" or 5.25" standards were used in
some servers as testing/backup media or in expensive workststions. My
drive comes from IBM Power Series 850 PowerPC workstation.
They were reliable, but quite slow and expensive.
Later magnetooptical disks evolved to GigaMO disks with enhanced
capacity (even 10GB) and Minidisc technology.