What significant achievement did the first hard drives accomplish?

The first hard drives significantly increased data retrieval speed through innovative designs, particularly the use of heads that floated above the disk surface. This technology allowed for quicker access to stored data, as the read/write heads could move rapidly and accurately across the spinning disks without making contact, which also minimized wear and potential damage. This floating mechanism was a pivotal advancement over earlier storage solutions, allowing for more efficient data access and improving overall performance.

While the other options mention notable concepts relevant to data storage, they do not accurately represent the primary breakthrough associated with early hard drives. The size of data storage and RAID integrations came later as technology evolved, and operating systems were essential for managing data on computers from the outset, making their removal irrelevant to the functionality of hard drives.