Dual actuator
A hard drive with two independent arm assemblies on one spindle, each able to seek over its own half of the platters, nearly doubling operations per second.
The problem it solves is that capacity has grown far faster than access speed. A 20 TB drive has as many heads as a 2 TB drive did, but ten times the data behind each seek, so IOPS per stored terabyte has fallen steadily. By splitting the platter stack between two voice-coil motors that move independently, the drive can serve two queues at once and appear to the operating system as two devices.
Seagate revived the idea with MACH.2 around 2018 and shipped it in the Exos 2X14. New it is not — a few early-1990s drives, such as the Conner Chinook, already had two actuators, but back then it was too expensive to justify. Now that every drive is enormous, the arithmetic has flipped.