CPU and RAM
The minimum RAM for Dota 2 is 2GB, while the recommended is 4GB. We definitely recommend that you have 4GB of RAM or more, as Dota 2 can easily use up 1GB by itself, which means that you will have little RAM left if you only have 2GB total.

Older CPUs, and very low-end CPUs, will be a bottleneck. If you want to get the full potential of your graphics card, then you need to have a decent dual-core CPU at least. Modern CPUs that are above the ~$100 mark, such as the i3 4130 or the FX 6300, should be fine.

If you have recently upgraded your graphics card but did not get as much of an improvement in FPS as you expected, check to see if your CPU is bottlenecking your performance. While this is true of Dota 2, it is also true of many CPU-bound games, particularly in the RTS genre. It is also one of the reasons that we always suggest having a balanced gaming PC, as that prevents bottlenecks to performance, no matter what game you play.