20 Megabyte Hard Disk Platter

A hard disk platter is a round, rigid magnetic plate that comprises part of a hard disk drive. Hard disk platters vary in size, the earliest drives, which were created in the mid-1950s, containing platters that were each approximately two feet in diameter. IBM’s 305 RAMAC (Random Access Method of Accounting and Control) could hold fifty of these large platters, for a total of 5 megabytes of storage space. Today, hard disk platters are significantly smaller, typically exhibiting diameters of about 3.5 inches or smaller. In order for computers to quickly retrieve information from a hard disk drive, the platters of the disks are divided into small magnetic domains, including cylinders, tracks, and sectors, which make it simple to locate the needed data. The information is actually read and written through the use of read/write heads that move across the surface of each platter, sensing and emitting magnetic impulses at the proper cylinder as the rotating object moves beneath it.

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