My iMac's internet is super slow!!!!

Question

     I have several devices that are conected to the internet at any given time. Including an iPhone 5, iPad 2, iMac 21" and several other computers. All my devices are connected to the internet through an Airport extreme. My internet download speeds are consistantly around 20-25 mbps, however when I try to load a web page on my iMac its like its 10 years ago and I am using dial up. And while waiting for my iMac to load the page if I try to load the same page on either my iPad or iPhone it will load instantly. Again all of my devices are connected to the same Airport extreme.
     At first I thought that it was Mediacom's crappy service but then I noticed that my other devices are working perfectly.
     Please help, this is extremely annoying considering I use this computer for work and I need constant and fast internet for my job.

Answer 1

Can you temporarily turn off Virus Barrier to see if this is slowing your system?
Also in your iMac's Applications folder, locate the Utilities folder, open it and look for and launch Activity Monitor.
Look at the Processes Tab and see if there is anything that is using a high percentage of your iMac's resources.
Also, it may just be you need to install more RAM memory.
if your iMac has a 3.06 Ghz CPU, then it is NOT a 2011 model, but a 2010 model iMac.
OS X especially versions 10.7 Lion and 10.8 Mountain Lion use a lot of CPU, GPU, RAM and hard drive resources.
The base 4 GBs that came with your iMac is not an ideal amount of RAM, but just enough to give sufficient operation of your iMac out of box.
OS X, by itself needs between 2-4 GBs of RAM to operate smoothly and efficiently on its own.
Start running extra applications on top of this and there will be more and more slow down of your iMac.
Your iMac can take up to 32 GBs of RAM.
I recomend installing, at least, another 4 GBs of RAM. If you can afford to install more, great then do that!
But you could just start with only an additonal 4 GBs of RAM.
You should see a speed improvement by just doubling the amount of RAM memory.
Here are the RAM specs for your 2010 iMac.
32 GB (Actual) 16 GB (Apple)
Memory Slots
4 - 204-pin PC3-10600 (1333 MHz) DDR3 SO-DIMM
You can purchase reliable Mac RAM online from Mac RAM vendors Crucial memory or OWC ( also known as macsales)
Good Luck!