Ofcourse, we all know how the mechanical parts of a hard disk are
supposed to work, and I wasn't really interested in those parts. My
interest was in the little PCB that's on the back of most HDs and
where the SATA and power connectors were located. This is what such a
PCB looks like:
You can see that there are about four chips on the PCB. This is what I found out about them:
This is a bit of DRAM. It's a jellybean part, with easy-to-find datasheets. The capacity of these chips range from 8MB to 64MB, and these sizes correspond to the cache size the hard disk is supposed to have.
This is the spindle motor controller. It's not a standard part, so datasheets are hard to find, but some of the controllers seem to have brothers and sisters that are a bit easier to find. ST Smooth controllers seem to be the most used ones; apart from driving the spindle motor, they also do power regulation and have some A/D channels.
This is a bit of serial flash. It's also a jellybean part, with sizes ranging from 64KB to 256KB. It seems to be used to store the program the hard disk controller boots up from. Some hard disks don't have this chip but have the flash internal to the HD controller chip instead.
These little devices aren't chips, but piezo-electric shock sensors. They can be used to move the heads somewhere safe when the HD experiences a mechanical shock, but more likely just set a bit somewhere to indicate your warranty is void because you dropped your HD.
And this is the bit where all the fun stuff happens: the hard disk controller. They are made by Marvell, ST and some other LSI companies. Some hard disk companies also make their own controllers: I've seen both Samsung and Western Digital do this. With almost everything else being a jellybean part, this is the device I was interested in.
Unfortunately, these parts are somewhat underdocumented. Saying the companies making the controllers aren't too kind on revealing information about them is an understatement: they don't even mention the existence of the part numbers on their sites! Unfortunately, the rest of the Internet isn't too helpful either: looking for datasheets only reveal datasheet-sites not having the actual PDFs and obscure Chinese sellers claiming to have the ICs.
So, no datasheets of the most important IC, that means we're stranded, right?