900 system requirements state that you will need at least 256 MB of RAM. In terms of game file size, you will need at least 40 MB of free disk space available. An Intel Core 2 Duo U7600 CPU is required at a minimum to run 900. Whereas, an Intel Core i5-650 is recommended in order to run it. The cheapest graphics card you can play it on is an NVIDIA GeForce GT 130. But, according to the developers the recommended graphics card is an NVIDIA GeForce GT 230.
900 will run on PC system with Windows 7 and up and upwards. Additionally it has Mac and Linux versions.