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IBM 305 RAMAC

The first commercial computer with a moving-head hard disk drive, announced on September 14, 1956.

IBM announced the 305 RAMAC on September 14, 1956. The first hard disk unit shipped the day before, on September 13.

Its IBM 350 disk system held 5 million characters on fifty 24-inch disks. Two access arms moved up and down and in and out under servo control. A RAMAC system with the 350 disk unit leased for $3,200 per month.

Why it matters

The RAMAC was the first commercial computer to use a moving-head hard disk for storage, the ancestor of every later hard drive.

Key facts

  • Announced September 14, 1956.
  • First hard disk unit shipped September 13, 1956.
  • Stored 5 million characters on fifty 24-inch disks.
  • Leased for $3,200 per month.
  • A full system filled a room about 30 by 50 feet.

Sources

  1. Wikipedia, "IBM 305 RAMAC", en.wikipedia.org/wiki/IBM_305_RAMAC, accessed October 14, 2026.
  2. Wikipedia, "IBM", en.wikipedia.org/wiki/IBM, background reading, accessed October 14, 2026.