Seagate Technology has released the new Momentus 5400 PSD hard drive, the first "hybrid hard drive" that puts 256 MB of non-volatile flash RAM in a 2.5-inch notebook hard drive to improve boot time and overall performance, reduce power consumption, and increase reliability. In essence, the flash memory serves as a large cache that can serve out commonly accessed data, enabling the drive to spin down more frequently and providing that data more quickly than it could be read from the disk platter. Because the drive spends less time spinning, power consumption drops, and because the drive is far less likely to be damaged while spun down, reliability increases at the same time. (Put another way, not using the drive makes it more efficient and more reliable - what a concept!)
Seagate's press release received quite a bit of play in the Mac press, but I'm sorry to say that there's absolutely no point in buying one for your MacBook Pro just yet. I confirmed with Mike Hall of Seagate that explicit operating system support is required for all the benefits of a hybrid hard drive, and the only operating system that provides such support right now is Windows Vista. Mike did say that Seagate hopes to increase the number of operating systems that support the Momentus 5400 PSD, but he didn't know of any support in the works from Apple. If you were to install one of these drives in a Mac now, Mike said it would work just like any other normal hard drive. And since the Momentus 5400 PSD drives are likely to be more expensive than normal drives, you should save your money.
That said, it's likely that we'll see a refresh of Apple's laptops in the next few months, and perhaps also the Mac mini and the Apple TV, all of which use 2.5-inch hard drives. It would be entirely within character for Apple to add hybrid hard drive support to Leopard, and to include the Momentus 5400 PSD in laptops as a way of increasing battery life and in the Mac mini and Apple TV to reduce power consumption and noise.
I think we'll be seeing more of this melding of solid-state storage with spinning-disk storage trend. Flash RAM prices continue to drop, with 16 GB Compact Flash cards as low as $128 and 8 GB SDHC cards at $65. I don't know how comparable those prices are to what's being used in the Momentus drives, since the 256 MB flash RAM that Seagate's using may be faster and thus more expensive than consumer-level cards, but Seagate can also undoubtedly reduce costs significantly by buying in quantity. If operating system support for hybrid hard drives becomes widely available, putting some flash RAM in a hard drive would seem like an easy win for everyone.