The drive spins a PET film disk at about 3000 rpm, 1 micrometre over a read-write head, utilizing Bernoulli's principle. The most popular system was the Bernoulli Box II, whose disk cartridges are 13.6 cm wide, 14 cm long and 0.9 cm thick, and have a similar external appearance to 5¼-inch floppy disks. Bernoulli disks come in the following capacities: 20 MB, 35 MB, 44 MB, 65 MB, 90 MB (late 1980s), 105 MB, 150 MB, and in 1994, 230 MB. There are five types of drives, grouped by the maximum readable capacity: 20 MB, 44 MB, 90 MB, 150 MB, and 230 MB. The interface is usually SCSI. Drives were available as either internal units, which fit into standard 5¼-inch drive bays, or as external units with one or two drives in a fully self-contained case connected to the host computer via external SCSI connector.
The disks have a switch to enable and disable write protection.
The original Bernoulli boxes came in capacities of 5, 10, and 20 MB. They were roughly 21 cm by 27.5 cm.
The Bernoulli Box drives were the direct predecessors of Iomega's popular Zip drive, introduced in 1994, which used a similar technology.