The whole power-of-10 thing for storage goes back forever-- to IBM mainframes and to the first hard drives used in PCs.

E.g. Seagate ST-506, first 5.25" hard drive.

"The total formatted capacity of the four heads and surfaces is 5/10 megabytes (32 sectors per track, 256 bytes per sector, 612/1224 tracks)."

612 * 32 * 256 = 5013504, or 5.01 megabytes or 4.78 mebibytes.