(Image credit: Getty Images / Nurphoto) Seagate , Toshiba, and Western Digital are the only remaining manufacturers of hard disk drives. They not only continue to produce these storage devices but are also actively advancing them as demand for HDDs rises again. While hard drives from these companies share many similarities, each relies on a different set of underlying technologies — distinct recording methods, actuator designs, platter materials, and magnetic alloys, among others — resulting in markedly different roadmaps. In this story, we examine these roadmaps and attempt to make sense of them. The state of the HDD market (Image credit: Toshiba) Hard drives have been around for nearly 70 years, and over 220 companies have produced HDDs since they were introduced in 1956.…