Between the proliferation of SSDs and the slow demise of HDDs, a strange hybrid of the two occurred that briefly kept the enthusiast community on tenterhooks: SSHDs. Solid State Hybrid Drives were a type of storage device that combined an HDD with an SSD, with the expectation that this would be a viable compromise between the two technologies given the cost of SSDs. Today, however, SSHDs are practically nowhere to be seen, and there are a few reasons for that.
First, SSHDs essentially offered high-speed caching because they contained a small amount of SSD storage. This meant that frequently accessed data could be accessed quickly while still benefiting from the cheap storage of a large hard drive. They were nowhere near as fast as true SSDs, but there were some minor improvements over HDDs that were noticeable.
4 Falling SSD costs
That was the big
When hard drives were phased out and SSDs were introduced, SSDs had one major drawback: cost. They would cost a fair amount of money for something consumers weren't convinced they needed. Even then, if you wanted faster boot times, it was common to buy a small SSD, install Windows on it, and then use the hard drive to store everything else.
However, SSD prices eventually went into freefall, and that meant they suddenly became affordable for the average consumer. That, combined with the speed benefits of an SSD, meant it was a no-brainer for people to just buy big SSDs rather than getting an SSHD or buying a small SSD just for Windows. Today, many of the best SSDs are still cheaper than some of the most mediocre ones were a decade ago.
3 More SSD capacity
You can now fit multiple terabytes in an SSD
Back when SSDs were on the rise, SSDs with as little as 32GB of storage capacity were not uncommon. These were very small, but also quite expensive considering the cost. 512GB was basically the upper limit for storage, and 1TB was practically unheard of. However, that has changed over time, and SSDs with multi-terabyte storage capacity are now available.
This was important because users didn't want to switch between multiple drives depending on what they were doing or where their Windows installation was. Now, with larger SSD sizes, it's easier to just install Windows and your programs and not have to worry about organizing them. HDDs still tend to offer more storage and are cheaper, but SSDs have improved a lot since then.
2 Lack of performance improvements
SSDs were significantly better
SSHDs, while faster than HDDs, still couldn't compete with a true SSD. They were more expensive and not really worth it for most people, and those who cared so much about performance just bought a cheap SSD to boot from instead. You didn't need an SSHD, and when SSD prices dropped and SSD storage started to increase, it just made sense to get an SSD rather than a hybrid of the two that was more HDD than SSD.
With an SSD it is still til todayone of the best upgrades you can make to any computer or laptop if it doesn't already have one. That wasn't really the case with an SSHD. That's how big the difference is between SSDs and SSHDs and between SSHDs and HDDs.
1 SSHDs were notoriously fragile
They were super easy to break
SSHDs have more components than a regular SSD or HDD, which means more can break. You have the fragility of the spinning disk of an HDD with the short lifespan of a cheap, old SSD, so the worst of both worlds. The SSD in these drives is constantly being written to, significantly more than a regular SSD, and that means that part of the drive can easily break due to excessive writes.
To make matters worse, many controllers back then didn't take this potential failure point into account. If the controller didn't detect that the SSD cache had failed, it typically wouldn't write directly from there to the disk, but would simply fail completely. This meant that the physical disk portion of the drive might be fine, but the SSD acting as the cache had failed, thus preventing the entire drive from being used.
In other words, you couldn't even rely on an SSHD to reliably store your data or be used for a long period of time. It was also a hard sell to consumers.
SSHDs never deserved the breakthrough
Honestly, SSHDs were pretty terrible and it's a good thing they never really took off. They had a lot of drawbacks and because they were budget-oriented, they often contained cheap flash storage that died pretty quickly and didn't provide much benefit. Now that SSD prices have come down, it's much more profitable to just have SSDs and the vast majority of enthusiasts probably do that these days.
Still, there was a weird time when SSHDs slowly started to grow a bit and I remember having one in my old PC. Eventually I went for a small SSD and a big HDD, but nowadays that's not necessary either.