What is the best upgrade/speed boost for my Apple Mac

I'm often asked; What is the best upgrade/speed boost for my Apple Mac?
 
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If your mac is feeling a bit sluggish, here is some advice from my years of experience.
 
Lots of people ask me "how can I speed up my Mac (or PC for that matter). Normally "IT guys" will start by saying "upgrade your RAM", while it's true upgrading the RAM will improve performance, it won't normally be by much. It is one of the easiest options because you just need to pop open a latch on an iMac or Mac mini to change the RAM. You should certainly upgrade your RAM if you have under 4gb or memory. 
 
But if you are practical and adventurous enough to open you computer up, I have a much better way to speed up any Apple MAC.
 
The easiest why to bump up your computers performance is to upgrade to an SSD. SSD is a slide state disk which has no moving parts and easily performs 10 time faster than your normal hard disk (HDD)

The process of speeding up you MAC by installing an SSD is quite simple:

1) Connect a new SSD externally to your Mac (you will need an external case, an external dock or a USB cable for external sata).
2) Use Carbon Copy Cloner to make a copy of you HD (hard disk) to your new SDD.
3) Carefully open your Mac (search for a video on youtube about opening your particular MAC model).
4) With your Mac open, carefully Just swap the HDD for the SDD.
 
Now when you power up your Mac you should notice a significant speed boost.
 
Bonus: After you have thoroughly checked your MAC is working perfectly with the SSD installed, you can then plug your old HDD externally and use it as a Time Machine drive or simply store it unplugged as a bootable backup.
 
PS. In my experience you don't really need to do a "fresh" install OS X. The Mac operating system is so well built reinstalling it from scratch is not really required like it is with windows.
 
Also I found Mavericks faster in general to other previous versions so once you have the SSD installed feel free to upgrade if you are using an older version.
 
This advice works if you run Leopard, Snow leopard, Lion, Mountain Lion, Mavericks or Yosemite.