The first commercial hard disk drive, the IBM 350 of 1956, was the size of two refrigerators. How many characters of data could it store?
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Answer
About 5 million characters
It weighed about a tonne, used fifty 24-inch platters, and was leased to customers rather than sold.
How to estimate it
Build it up from the geometry. Fifty platters have 100 recording surfaces. Each surface carried 100 concentric tracks. An inner track about 40 inches around, at 100 bits per inch, holds 4,000 bits, and with 7 bits per character that is about 570 characters. 100 × 100 × 570 = 5.7 million. IBM's rated capacity was about 5,000,000 characters.
Source: IBM Archives
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