While 1GB is the bare minimum, 4GB of RAM is strongly recommended to handle the Unity Editor and an IDE like MonoDevelop simultaneously. Graphics: DX10 (Shader Model 4.0) capable GPU. Important Tips for 32-Bit Users Unity download archive
Go to the official Unity Download Archive . Unity 3d 32 Bit Download Free
Click on the Unity 5 tab to see all legacy versions. Choose a Compatible Version: While 1GB is the bare minimum, 4GB of