Energy assisted technologies like HAMR and MAMR have made it possible for the manufactuers to produce higher capacity drives, but a better drive is as much about higher performance as it is about capacity. If only the areal density increases with no increase in the transfer rate, you would have a bigger but slower drive.
One of the many ways to increase the performance is to have multiple independent actuators, covering different areas of the platter at the same time. This would increase both IOPS and transfer rates.
Traditionally hard drives have been Single Actuator , with IOPS not exceeding 100 for a 7.2K RPM Drives. Muti Actuator technology in contrast would have multiple actuators, creating multiple data channels and for the same 7.2K RPM drive , a dual actuator will yeild 200 IOPS through parallelism.
An Array with multiple drives has the combined IOPS of the drives in theory ( if the IOPS are fixed at 100 then an array of 2 x 8TB would have 200 IOPS , against 100 IOPS of a single 16TB Drive) A Multiactuator drive mimics this array. A multi actuator drive is the equivalent of having multiple drives with Multi Actuators Just like an array. Needless to say the power consumption on multi actuator drives will be higher than a single actuator drive. The total power consumption would still be lower than using 2 drives though becuase all the other subsystems consumption remains same and only the power consumption of actuator is doubled.
Though hard disk drives offer the lowest cost per TB, they lag behind SSDs in both IOPS and transfer rates. Multi Actuator technology is a step in this direction of incresing the performance.
Seagates Double Actuator Mach.2
Seagate MACH.2 technology uses two independent actuators per hard drive, doubling the transfer and IOPS. Within a drive, each Actuator address one half of the capacity of the drive - one taking care of top half, and other taking care of the bottom half of the read/write heads.
Seagate claims to have started working on this in their Exos 2X14 hard drives already and will make it available in multiple SKUs for enterprise users.
Western Digitals Multi Actuator drives
Western Digital has also been working on their multi actuator drives. They have not given it a name like Seagate has, but WD is said to be working on the technology for sometime for their large capacity drives.
Right now, multi actuator technology will be limited to 2 actuators, but In future, there may be more than 2. There may be 4 actuators for example each one taking care of 25% of the drive read/write heads. Multi actuator would be an important technology in increasing the HDD throughput.