Information Technology Reference
In-Depth Information
The first disk drive
Prior to the invention of magnetic disks, magnetic cylindars, called drums, were used
for on-line storage. These drums spun on their axes and typically had one head per
track. So, there was no seek time to access a block of data; one merely waited for a
block to rotate underneath its head.
By using spinning disks instead of drums, the magnetic surface area, and hence the
storage capacity, could be increased.
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The first disk drive, the IBM 350 Disk System (two are shown in the foreground of
this photograph), was introduced in 1956 as part of the IBM RAMAC (“Random Access
Method of Accounting and Control”) 305 computer system. The 350 Disk system stored
about 3.3 MB on 50 platters, rotated its platters at 1200 RPM, had an average seek
time of 600 ms, and weighed about a ton. The RAMAC 305 computer system with its
350 disk system could be leased for $3,200 per month. Assuming a useful life of 5
years and converting to 2011 dollars, the cost was approximately $1.3 million for the
system—about $400,000 per megabyte.
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