from fdisk(8)
DOS MODE AND DOS 6.X WARNING
Note that all this is deprecated. You don’t have to care about things like geometry and cylinders on modern operating systems. If you
really want DOS-compatible partitioning then you have to enable DOS mode and cylinder units by using the '-c=dos -u=cylinders' fdisk
command-line options.
... did people in the past partition their disks with circular geometry?? what???