Apple's take on this is the Fusion Drive. The principle is the same, only there is a lot more of the flash memory. The standard Fusion Drive that Apple have offered for several years consists of 1TB regular mechanical storage plus 128GB of flash memory - 16 times as much as in a SSHD from the likes of Seagate or Toshiba. The effect of this can be quite dramatic, enabling the computer to operate as though it just had fast SSD storage. In recent years this has almost constituted the Holy Grail of storage, although Apple's premium prices and the failing price of pure SSD drives has negated matters somewhat in the past year or two.
What most people do not realise is that the Fusion Drive is not actually a physical drive at all, at least not in the sense that a SSHD drive is. Rather it is two separate physical drives, one a normal HD and the other a normal SSD. Rather than being physically joined, they are joined together logically in software only. Mac OS X has the hooks built-in to it to make this happen, which is partly why it works so well. And frankly, most Macs need this assistance as boot times for OS X are dreadfully slow. The SSD drive is PCI-E based rather than regular SATA, meaning it runs at around 2-3 times the speed. Apple charges a premium of £160-£200 for a Fusion Drive; in reality, what you are buying is a high-performance 128GB SSD blade which has a typical retail price of around £70 (no wonder Apple is so profitable!).
Last year, Apple refreshed their iMac line with a new model. A Fusion Drive is available as an option for just £80, which sounds a lot more reasonable. But there's a catch (I almost wrote "there's a cache"), as the SSD component has been reduced from 128GB to just 24GB. This is still enough to hold OS X and some apps, giving that all important boost to startup times. But as might be expected, the overall effect on system performance is now far less dramatic. A 24GB PCI-E SSD is not the sort of component you can readily buy, but 30/32GB ones costs around £25 retails so Apple is still making a lot of money. It's also interesting to note that Lenovo were offering a 24GB SSD cache on some of their laptops as far back as three years ago.
Just in case someone thinks this article is a spot of Apple-bashing, it's worth pointing out that it is being written on a Mac Mini...