My poor macbook has been suffering too much in these last two years, so I decided to upgrade to a new SSD hard drive (a Crucial M550 512gb) and I also took advantage of the situation to do a clean install of the latest newborn OS of Apple, Yosemite.
First, I made a USB bootable installer of Yosemite by downloading (without installing) the Yosemite App from the App Store. Then I ran this single line of code in the terminal.
(obviously, you’ve got to replace YourUsbName with the name of your flash drive)
1sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/YourUsbName --applicationpath /Applications/Install\ OS\ X\ Yosemite.app --nointeraction
This took the time of more than one cup of tea, especially since I was on USB 2.0 (I recommend doing it with a thunderbolt hard drive, instead of a usb one).
After that I manually unscrewed everything (a Philips PH000 and a Torx T6 are you’re best friends), changed the drive (many thanks to this youtube video and ifixit.com for the detailed guide on how to do this correctly) and finally rebooted with the usb flash drive inserted while pressing the option (alt) key on the keyboard.
I then choose Disk Utility, formatted the new SSD to a Mac OS Extended (journaled) filesystem and finally installed Yosemite (which also took some time).
Now I get around 6 second for boot, which is pretty awesome.
This is my SSD score.