This idea occurred to me a few weeks ago and I just wanted to see what others with more knowledge on it think. I haven't been a regular on this board, so forgive me if the idea has already come up.
Here it is:
Current hard drives have one head per platter surface. What would be the consequences of having more. There is room around the platter with current head assembly designs for probably 3-4 head assemblies without them interfering with one another. My thoughts are that the drive could then access 2, 3, or 4 files at once. For example, one head could be accessing the swap file while another is accessing data for the program you are running, while another is writing something else. Also, it could operate something like a striped raid such that all the heads could be writing parts of the file at the same time. Of course that would leave the file rather fragmented. Speaking of file fragmentation, defragging would be a lot faster.
With regards to reliability, I would expect the reliability to be somewhat lower because there are more parts to fail. However, I don't think it would be difficult to design logic that could detect if one head assembly failed and then take that assemly out of action and leave it parked. Performance would decrease, but the drive would still operate.
One major problem I could see is that current interface technology may not be able to handle it. I don't know if current interfaces would be capable of managing multiple data streams. Maybe it could be done by using 1 cable/connector per head assembly, or perhaps the drive electronics could make it work. Or, it may require an entirely new interface.