TCP is a protocol that is used for networking and it determines and regulates the amount of data (traffic) that can be transferred at one time across any type of media or host.

When Windows is installed, the registry has been pre-set with a pre-determined value of how much data can be transferred via the network at any one time. So, by default all Windows with the same type of Internet connection will basically run at the same speed.

What a TCP Optimizer does, is go in and change those settings in the Windows Registry to allow for a larger amount of data to be able to be transferred at any one time.

Now a lot of optimizers will allow you to go in and set your bandwidth settings personally. (Note: I only recommend doing this if you have a lot of experience in the networking industry), because changing these settings in the registry can not only slow your networking speed, but if you change the wrong setting, it can completely screw up the entire operating system.

There are many different TCP Optimizers out there that will automatically change all the settings for you. All you have to do is input the type of Internet connection that you have (cable, DSL, dial-up, etc).