IIRC - and I did programming on some of the first IBM PCs when I was in high school in 1983 - IBM’s original 5 1/4 inch floppy disk drive (FDD) capacity was a tiny 360kb. Yes, it was truly amazing that DOS could run from a single 5 1/4 inch floppy disk.
When the PC/AT came out, the 5 1/4 inch FDD storage capacity grew to 1.2Mb - not exactly an even multiple of 360kb. That’s one of the reasons why I remember the storage numbers on these drives; the other is that I sold a LOT of floppy disks to the Computer Science students at my university, and I had to learn to ask if the disks were being used on a computer in the dorm room (likely the 360kb storage) or on one of the PC/AT machines in the computer lab. Sometimes, the answer was “both!”