The original IBM RAMAC disk platters were several feet across:
"The 350 Disk File consisted of a stack of fifty 24" discs that can be seen
to the left of the operator in the above picture. The capacity of the entire
disk file was 5 million 7-bit characters, which works out to about 4.4 MB in
modern parlance. This is about the same capacity as the first personal
computer hard drives that appeared in the early 1980's, but was an enormous
capacity for 1956. IBM leased the 350 Disk File for a $35,000 annual fee."
The Control Data 808 disk drive also used platters that were at least thet
large.