There is no doubt that when compared to a mechanical hard drive, the new solid state drive (SSD) technology is by far superior in terms of speed. Data access and throughput can be well above 4x faster than a contemporary mechanical drive, and using it as your main boot drive widens a major bottleneck, resulting in exceptionally quick boot-ups, application launches, sleep and wake events, and shutdowns. Beyond speed, the drives also have a number of additional perks, including cooler operation than most mechanical drives, power efficiency resulting in longer battery life for laptops, silent operation, and higher tolerance for abuse since there is no need to protect moving mechanical components.
Unfortunately along with its benefits, SSD technology is currently very pricy, to the point where it may not be feasible to upgrade a system with a comparably sized drive. This is especially true if you need to maintain large storage capacity on your system. For example, the average price of a 500GB mechanical drive is currently around $40 whereas a 500GB SSD is over 20x more expensive at around $850.
Because price may be a limiting factor for upgrading, one option is to create a hybrid SSD environment to give yourself the best of both worlds: a small and fast SSD drive to hold your system and applications, and a larger mechanical drive to hold your larger personal data. Apple offers this as a configuration option for new iMac and Mac Pro systems, but so far Apple's laptops have not had the capability of holding more than one hard drive, at least with the default configuration.
To overcome this limitation for the MacBook Pro, beside dishing out the money for a large SSD you can take two routes. The first is to use a larger external drive along with a smaller internal SSD, but this may not be the best option (especially for laptops) because external drives are slower, more prone to breaking, and will require you to lug them around to keep attached to your system.
The second option is a more practical one, which is to replace the optical drive in the system with a bracket that can hold a second hard drive in its place. This will allow you to take advantage of a small and cheaper SSD drive, while maintaining a second larger mechanical drive in the system. Being an unconventional approach this may seem a bit odd at first, but there are three reasons why someone would want to do this:
Rarely use the optical drive
Even though optical media is still widely used, most content is available via download and can be placed on flash drives as disk images if you need to install it. Even Apple's next operating system, Lion, will be available only as a download from the App store that will install without the need for optical media. Movies and music are all available online, and many times people end up using their optical drives only for backup purposes instead of for active daily use. This is not to say people do not use them, but rather that the optical drive is becoming progressively less used and you can get by without it.
Need for speed
Even the fastest mechanical drive is far slower than SSD options, so the need for a snappy OS experience requires more throughput, especially as applications and system software gain larger and larger footprints. Even items like system icons have gone from 16x16 or 32x32 pixels to 512x512 pixels or higher to make the OS look pretty, and all these larger resources together take more drive space and RAM, and therefore require more throughput to load and manage in memory. As a result, even by compensating and getting more RAM, a system will still be paging large amounts of RAM data to the hard drive, and speeding this process up will greatly increase RAM efficiency.
Cost vs performance
As I mentioned above, SSD prices are quite high, but in addition, the majority of storage on large SSD drives will go relatively unused for most people, and even Intel has shown that people can get by fine with smaller SSD sizes. In Intel's latest Z68 chipset, the SSD caching technology uses an SSD drive of up to 60GB to store frequently accessed items stored on slower mechanical drives. What this demonstrates is that most people do not usually have more than 60GB of regularly accessed items on their hard drives, and therefore should be able to get a fast experience by implementing a smaller SSD drive than one that will hold all of their data.
For my uses I meet all of these criteria, so recently I decided to give this setup a try in my MacBook Pro. There are a variety of SSD manufacturers out there, and the options for a drive mounting bracket include OptiBay and Other World Computing. Other World Computing has been offering upgrade options and add-ons for Mac systems for over 20 years and has gained a reputation for offering well-made and reliable options for Mac systems, so I was content with trying three of the upgrade kits they offer:
The DIY "On-the-Go" Laptop Drive Upgrade kit
This kit is basically a hard-drive upgrade that includes an external enclosure to turn your old hard drive into an external drive. Optionally you can just use the included drive with the enclosure to get a larger external drive to use (though this would defeat the purpose of having purchased the upgrade drive for your system). The kit also comes with a Torx and Phillips driver set along with some plastic pry bars that help in assembling the enclosure and installing the drive on your system. The kit I chose included a 750GB Seagate Momentus 7,200rpm hard drive.
I primarily chose OWC's "On-the-Go" option because it has options for supporting multiple drive interfaces (combinations of Firewire 400/800 and USB 2), OWC also offers a "Express" enclosure that is either USB 2 or USB 3 (though USB 3 is not yet available from Apple on Mac systems). Keep in mind you can use any 2.5-inch external drive enclosure for this upgrade, but bundling it all with one purchase might be an easier route.
Data Doubler Kit
This kit is the main part of the upgrade because it allows two hard drives to be put in the system at once. It offers a sturdy mount for 2.5-inch drives in the optical bay of the MacBook Pro (though there are options for the MacBook and Mac Mini as well). This kit can come with just the bracket, or you can include your choice of mechanical drive or SSD. For my hybrid setup I chose the kit with the 115GB Mercury Elite SSD.
After installing the Data Doubler you are left with the bare optical drive that came with your system, so instead of putting it on the shelf or auctioning it off online, you can turn it into an external drive by using OWC's value-line superslim optical-drive enclosure. While more of an optional component in my point of view, OWC does offer it at a discounted price when you purchase the Data Doubler kit.
With these three options, the total price ends up being $449.97, whereas doubling the SSD capacity by only getting a single 240GB bare drive upgrade would be almost exactly the same price at $449.99. Granted, prices will always fluctuate and SSD prices will undoubtedly drop, but with the upgrade kits I got ample SSD storage for the OS and applications I use, and the option to either keep my original drive for data storage (and use the 750GB drive for external storage), or upgrade to the 750GB drive that came with the DIY kit.
In order to take full advantage of the upgrade, I installed both the 750GB drive and the 115GB SSD in the system, which results in a full 865GB of internal storage, along with both an external hard drive and an external optical drive.