When hard disk drives initially made their way into microprocessor-based computers, they used magnetic platters up to 8 inches in diameter. Because that was the largest single component inside the HDD, it defined the minimum width of the HDD housing—the metal box around the guts of the drive.

When solid state drives first started replacing HDDs, they had to fit into computer chassis or laptop drive bays built for HDDs, so they had to conform to HDD dimensions. However, there’s no requirement for the SSD to match the shape of a typical HDD form factor and that's becoming more obvious as of late.

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