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Limits RegistryThe IBM 305 RAMAC, introduced in 1956, was the first commercial computer system to use a moving-head hard disk drive for storage, holding 5 million characters (about 3.75 MB) across fifty 24-inch platters at an areal density of roughly 2,000 bits per square inch — the historical starting point against which today's hard drives, storing over a trillion times as much data per square inch, are measured. The RAMAC unit itself was roughly the size of two refrigerators and had to be shipped by cargo aircraft due to its size and weight.
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The IBM 305 RAMAC, introduced in 1956, was the first commercial computer system to use a moving-head hard disk drive for storage, holding 5 million characters (about 3.75 MB) across fifty 24-inch platters at an areal density of roughly 2,000 bits per square inch — the historical starting point against which today's hard drives, storing over a trillion times as much data per square inch, are measured. The RAMAC unit itself was roughly the size of two refrigerators and had to be shipped by cargo aircraft due to its size and weight.
The areal recording density of the IBM 305 RAMAC, introduced in 1956 as the first computer system to include a moving-head magnetic hard disk drive, establishing the historical floor from which nearly seven decades of subsequent areal-density scaling is measured.
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Limits Registry. LR-IBM-RAMAC-FIRST-HDD. Lowest areal density of the first commercial hard disk drive. 2026.