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Strange Medieval Devices
In the late 1970s and the 1980s, the best choice for high-performance, high-capacity storage was so-called SMD disks.
The SMD interface was only normalized as ANSI X3.91M-1982 in, well, 1982, after five years of work, and was later revised in 1987; this revision can be found on Bitsavers.
Although other storage technologies appeared during the 1980s, such as ESDI (standardized in 1984) or SCSI (standardized in 1986), the highest capacity disks were all using the SMD interface.
SMD disks were first using 11" platters, later 8"; and with a nominal speed of 3600 rpm, thus 60 rotations per second (although Fujitsu later deviated from the norm and had a few drives spinning even faster, at 3961rpm), it took a noticeable amount of power to spin these disks up (and a smaller one to keep them spinning, which one would notice when receiving the bill from the electricity company).
These disks would also, of course, weigh as much as a dead donkey, if not two. While 8" models could be carried carefully by one person, moving 11" disks around usually required the use of some form of carriage.
SCSI standard documents (click for a larger picture). SCSI standard documents (click for a larger picture).
It was thus no surprise that Sun Microsystems would ship its high-end servers and workstations with SMD disks, using Xylogics controllers.
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