The HDD or hard drive is up there with CPU and RAM as one of the most recognizable pieces of computer hardware. Even people who aren't tech enthusiasts have probably heard of hard drives, even if they don't know exactly what it is. Although the HDD may seem quaint and outdated, it's actually a fairly complex piece of technology even by today's standards. Here's everything you need to know.
A high-capacity but slow storage device for PCs
The hard drive (or hard disk drive, which is where HDD is derived) is a veteran of the computer world. It's one of the few components in a PC that's mechanical, meaning it uses moving parts in analog operation, as opposed to something 100% electrical or digital, which is what the industry has trended towards. The HDD is one of the oldest kinds of computer components still sold today, and it's also one that has seen relatively little change compared to other components like CPUs and GPUs. That's not to say hard drives haven't gotten better; they have, and they offer more capacity than ever before.
There are two basic components to an HDD: platters and an arm. The platters or disks are the physical things that store data, and they're usually made of something non-magnetic like glass. Being non-magnetic is important, as these platters are covered in a magnetic material, and it's the altering of this magnetic material that can create data. The arm wields a reading and writing head, which physically interacts with the magnetic material to read and write data. The arm isn't the only thing moving in an HDD, though, as the disks are able to spin in order to get the read/write head where it needs to be more quickly.
For many years, improvements to HDD technology have largely focused on capacity since performance basically can't get any better. The most recent innovation in HDDs was Shingled Magnetic Recording (or SMR). Basically, each platter is made up of circular tracks, just like you'd see for racing events, and in a normal HDD these tracks don't overlap. An SMR drive allows these tracks to overlap, thus massively increasing capacity, but the catch is that any time data is written, it writes over two tracks. Data has to be shuffled around in order to prevent data loss, which massively slows down performance.
Since the 2010s though, HDDs haven't been the only storage device in town. SSDs are basically the mirror opposite of the HDD, and where HDDs offer a high capacity for a low price in a physically large and mechanical device, SSDs offer much higher performance in a small and 100% digital form factor, whether you're talking the best of the best SSDs or even a model that's mediocre.
Should you even buy an HDD anymore?
Financially, the hard drive industry is in a decline, especially since 2022 which saw sales for HDDs drop by nearly 50% as compared to 2021. Laptops have more or less stopped using HDDs, mostly because as a mechanical device, the HDD is vulnerable to faulty operation when in motion, which is a problem for a mobile device like a laptop. Even in relatively budget PCs, SSDs are popping up more and more as SSDs become cheaper and cheaper. This makes it hard to justify buying an HDD, but it's not time to declare it extinct yet.
Firstly, at the time of writing, SSDs are hitting rock bottom prices, but it's likely this won't hold. Pretty much every company making SSDs is winding down production in order to reduce supply, which will make prices go up. HDDs on the other hand won't be getting more expensive (probably), and although SSDs will still likely have a decent value for capacity, HDDs should offer the best deal by a significant margin.
Additionally, HDDs can generally achieve higher amounts of storage than SSDs, at least for the average user. 8TB is the limit for individual SSDs, but HDDs can hit up to 21TB, nearly three times more. Of course, an HDD is much larger than an SSD, but HDDs use old SATA cables rather than M.2 slots like most modern SSDs, which in this case is an advantage for the HDD, as most motherboards tend to have more SATA ports than M.2 slots. There are ways around this for SSDs, such as using a PCIe x16 card that can carry multiple SSDs or using SATA SSDs (which are slower than NVMe drives), but HDDs undeniably provide a simpler solution because you're just using SATA ports, and they can offer a lot more storage than a SATA SSD for a lower price.
Finally, if you're using an HDD just to store data rather than actively use it, the poor performance won't really matter. An HDD should never be your primary drive and they're not even suitable for storing games anymore (which is best done on an SSD), but long term storage of other kinds of media and backing up data is exactly what HDDs are good for.
To be clear, HDDs are pretty niche these days and most people would be better off just sticking to SSDs, even the cheap ones. There is still room for HDDs in modern PCs, however, especially if you're aiming for more storage rather than more speed.