Discussion  - 
World’s First Hard Drive (5MB) (Nov, 1956)
"RAMAC, IBM’s newest data processing system, needed a unique memory storage system. The heart of this new idea: magnetic disks, played and replayed like the records in coin-operated music machines!
Here’s how it works: Information is stored, magnetically, on fifty disks which rotate at 1200 rpm. These disks are mounted so as to rotate about a vertical axis, with a spacing of three tenths of an inch between disks. This spacing permits two magnetic heads to be positioned to any one of the 100 concentric tracks which are available on each side of each disk. Each track contains 500 alphanumeric characters. Total storage capacity: 5,000,000 characters. The two recording heads are mounted in a pair of arms which are moved, by a feed-back control system, in a radial direction to straddle a selected disk.

This new system promises memory storage possibilities never before accomplished."
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Was it marketed as "5 MB"? I'm curious if the powers-of-ten vs. powers-of-two thing goes all the way back to the very first unit.

Strict SI would say 5.0e6 characters is 5 MB, or 4.77 MiB.
Storage was counted to the base ten. Random access memory was addressed directly by physical address lines, so base 2. It was purely because it was easier that way.
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