The quick answer is yes, you can boot from an external drive. With the external drive connected, hold down the "Option" key while tuning on your computer. Continue to hold it down until the options for selecting your drive appear. You can then click on the drive you want to boot from.
Having said that, I'm not very clear on what you are explaining. You can't "wear out" the internal "hard drive ports". The transfer of data through the port will not wear it down. Running your OS from an external drive will be much slower. Frankly, using an SSD for this would be pointless. You only have two options, USB 2.0 or Firewire. Neither of which come remotely close to being able to transfer data as fast as the internal SATA port. You would not even to get the full speed of a 5400RPM hard drive. Your system will take much longer to boot and will run much, much slower (especially if you have been using an internal SSD).
You're best to keep the SSD as your internal drive and get an external drive for data, etc. if you need the additional space.
I may be misunderstanding what you're trying to do... If so, please clarify.
I want to boot my computer using one of my internal hard drives using an external hard drive enclosure so that I do not wear out the the hard drive ports
I'm not sure what you mean about wearing out the hard drive ports. However, to answer your question, yes, you can boot from an externally connected hard drive. With the hard drive connected to the system, go into System Preferences, click on startup disk, and choose to boot from your external hard drive. The system will remember that choice as the boot drive.
By wear out I mean connecting and unconnecting the hard drives. I have specific uses for each and I would like to swap them more often than once every 1-6 months. It doesn't have to do with not having enough data space. I would prefer to be able to use both of them daily
That piece they are holding with their left hand in step 9; that is what I would like to avoid ruining by swapping hard drive back and for on a daily basis. http://www.ifixit.com/Teardown/MacBook+Unibody+Model+A1278+Teardown/589/2
You might want to think about a powered USB hub.
The hub is connected to the Mac, and gets its power from a wall outlet. All your usb devices are plugged into the hub. Since a hub can have as many 12 ports, there is no need to unplug anything. But if you do, you unplug at the hub, not the Mac.
The piece shown in step 9 is inside the computer. You do not connect / disconnect anything there unless you are replacing an internal hard drive.
I am confused as to why you are suggesting a powered USB hub.
Yes, that part is for using an internal hard drive and as I stated that is the one I am trying to avoid wearing by daily swapping. Not only is it an inconvenience to swap them, but it is not an activity that is usually expected to be performed by most users, so likely this part is not meant to be used for that and that would make it not built for multiple hard drives swaps making it prematurely wear out.
... that part is for using an internal hard drive and as I stated that is the one I am trying to avoid wearing by daily swapping. Not only is it an inconvenience to swap them, but it is not an activity that is usually expected to be performed by most users, so likely this part is not meant to be used for that and that would make it not built for multiple hard drives swaps making it prematurely wear out.
That is exactly correct. We do not do that.
It is not necessary to get inside your computer to connect a hard drive. You can connect a second (or third, or even more) drive externally. And if the drive is correctly formatted, you can boot from it. An external hard drive enclosure costs less than < $10. You install the drive in the enclosure, and you can connect it externally to a usb port on the computer.
A typical enclosure for a SATA laptop drive looks like this:
In summary then, keep one drive inside the computer. Always. Use any other drives you need as externals. If you have many external usb devices, plug them into a powered hub. This way nothing needs to be regularly connected and disconnected.
I see what you're saying. I certainly would not want to regularly connect/disconnect the internal drive. That cable isn't really designed for that. If you could give us a little background as to why you're swapping these drives around, we might be able to respond to you a little better. That being said, you can certainly boot from an external drive. Your system will run quite a bit slower however. I would suggest that which ever drive you want to be your main drive (the one you'll be using most often)... keep that drive internally. Then use an external enclosure to swap out any other drives you want to use. If you're feeling particularly adventurous (and you don't need your optical drive), you can actually get a kit that will allow you to put a second hard drive where your optical drive is. It's something like this (but you'll have to look around for a kit specific to your model):
If you have to swap around more than two drives, I probably wouldn't recommend this as you'll still need an external solution and if you're going to do that, you might as well keep your optical drive. This connector is a bit more robust than the ribbon cable connecting to the shipped drive.
Partitioning woudl bring up a whole other line of questioning.
I like to use different drives for different things.
"keep that drive internally." I plan on it.
Optical drive conversion, that is an interesting idea. If my optical drive ever broke I would consider this. It would be nice if it told you what speed it was capable of transferring with this conversion, never mind it says "(3Gb/s) speed"
Now I have to decide which hard drive enclosure to get.