Being a child of the 70’s and retro computer enthusiast, one of the things that I learned early in my computer technology journey was just how high precision hard disk drive (HDD) technology was and why you should never attempt to take one apart. (if you want it to continue working anyway)
An HDD works by hovering a tiny set of magnetic coils (the read/write head) over the surface of a spinning disc coated in iron oxide. For this to work effectively, the head needs to be positioned extremely close to the surface of the disc. Back in the 1960s when these devices were a relatively new invention, the discs and heads were quite large, but the gap between them was a relatively tiny 6 microns! (that’s 6 micrometers, or 6 thousandths of a millimeter!) Today that gap is an order of magnitude smaller at just 5nm! (5 nanometers, or 5 thousandths of a micrometer!) To put into perspective just how small that is, a strand of DNA molecules is just 2.5nm in diameter or half the distance a modern hard drive’s head floats above the surface of a disk spinning at between 5,000 and 10,000 RPM for typical applications today. That takes an incredible degree of engineering and manufacturing precision.
You may wonder how it is that the head stays in perfect alignment just above the surface of the disk platter? The secret is air. As the disc spins it flings the air molecules inside the drive in the direction of rotation and this in turn creates a cushion of air molecules the head(s) float on without actually touching the disc itself. This effect has a drawback though, it requires a completely pristine environment free from any particles of debris such as dust or other contaminants. This is the reason hard drives come as a brick-shaped metal enclosure sealed with multiple screws, both to protect the sensitive internal mechanism and to keep out contaminants.
This leads to why it bothers me so much to see youtubers taking older drives apart, often just to check the mechanisms are in good working condition. The problem is that even if you manage not to break anything, you’re still corrupting the environment by breaking the seal and introducing dust into the formerly pristine environment of the drive’s internal mechanism. The average dust particle is only about 5 microns or so, but that’s plenty big enough to crash the heads of these older drives from the 1980s and early ’90s which typically floated their heads at about 70nm from the surface of the disc. Even a 1 micron dust particle would be massive by comparison at 1000nm, more than enough to knock the head off it’s cushion and slam it into the surface of the disc. A head crash can cause serious physical damage to the both the magnetic coating of the disc and to the read/write heads. Each instance creates more debris and spots on the disc where data is no longer readable.
So, with all that said, if you’re a retro hardware enthusiast, please think twice before taking apart that old boat anchor of a hard drive before determining if it works or not. It’s not like there are a ton of working examples out there in the first place. We should preserve those that may still work instead of just assuming they’re all trash.
