I remember some 5.25-inch full-height[1] SCSI drives from the 1990s had lots of platters. The Seagate ST410800 had 14 platters and 27 heads[2].
According to Wikipedia[3], the IBM 350 was the first disk drive, and it had 52 platters!
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[1] i.e. twice the height of a "regular" 5.25-inch drive bay in a PC case, which is actually half height.
[2] See p. 14 of the spec sheet (https://www.seagate.com/staticfiles/support/disc/iguides/scs...) and a YouTube video (https://www.youtube.com/watch?v=_LhneJ2u8WQ) which says 13 in the description but shows 14 in the video.
[3] See https://en.wikipedia.org/wiki/History_of_IBM_magnetic_disk_d... . But if you follow their link to IBM's info (https://www.ibm.com/ibm/history/exhibits/storage/storage_350...), IBM says 50, not 52. I guess it's hard to count hard disk platters?
This is insane, yet it works. Reading the comments brings another gem:
"Say, for whatever reason, power is cut off during the write process on a large data batch. The System-on-a-Chip (SoC) of an OptiNAND drive — in under a second — will use the rotational power generated by the already spinning disks inside the drive to power internal capacitors until any cached data transfers to non-volatile NAND. Previously, without an iNAND component, that data would potentially be lost."