Speed is affected by a number of things...
First it's what bandwidth you have with your ISP, the higher the bandwidth the faster it goes.
Past that you are limited by your router (it can only move information so fast - if it's an old one then you will notice), also limited by your computer.
On your computer you're limited by your network connection (built in generally isn't super-fast, but it's still a good speed), and then your OS settings and processor (your computer can only handle and move the information so fast as well).
Oh, and another thing is the distance from your ISP (if it's not cable). For DSL the further from your ISP you are the slower your speeds are, if you are at the end of the area (like I am) then you will notice things going slower.