Hello SIGCIS, My new candidate for largest hard drive is the Librascope Disk File, as used at SAIL. According to this letter from Ed Feigenbaum, only two were produced. Stanford acquired one of them for $300K in 1967, but a year later a "massive malfunction" destroyed half of its capacity, leading to a lawsuit settled out of court. In 1976 it was decommissioned, but at least one of the platters was saved and displayed. https://exhibits.stanford.edu/feigenbaum/catalog/ct397kv6234 According to these pictures of the display, http://infolab.stanford.edu/pub/voy/museum/pictures/display/1-MD-MemDisk2.ht m it was a "head per track" unit (i.e. more like a flat drum memory than a regular disk) which would solve the problem of large access times moving a head over such a large disk. The overall drive had six platters and weighed 5,200 lbs, to store 1,120,665 32-bit words (ie about 4.27MB) per side. So about 50MB total. An exhibit page at CHM documents what seems to be a platter from the same drive, claiming a 5 foot diameter (i.e. approx.. 60 inches). https://www.computerhistory.org/collections/catalog/102682858 On the other hand, an ebook about the SAIL DART archive gives a 4 foot diameter (i.e. approx.. 48 inches). https://www.saildart.org/simple/booklet/SAILDART_PREVIEW_2020_0330_good.pdf Both are comfortably larger than the 39 inch diameter for the Bryant drive. And as both platters are still around, someone should be able to make a precise measurement for the record books. Best wishes, Tom