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The Hard Disk Drive


In 1956 the most successful data storage method was invented, the hard disk. This is still a magnetic storage technology but instead of using coated tape it uses coated metal discs called platters. There are many of these discs mounted on a motor spindle which spins them at high speed. The read and write heads only have to move the radius of the stack. This means hard disks are not sequential access but random access, they can jump straight from A to D without having to pass B and C. The first commercial hard disk was produced by IBM, the 305 RAMAC (Random Access Method of Accounting and Control). It used fifty 24 inch aluminium platters, weighed almost a ton and was the size of two refrigerators.  It had a relatively high storage to area ratio of 90,000 bits/in2. But had a low storage to cost ratio of 5 mega bytes (41943040 bits or individual states) for $35,000.














































Punch Cards and Valves


Magnetic Tape


The Floppy Disk


The Compact Disk




Magneto-Optical Storage


The future