function checkOS()
{
var OSName="Unknown OS";
if (navigator.appVersion.indexOf("Win")!=-1) OSName="win";
if (navigator.appVersion.indexOf("Mac")!=-1) OSName="mac";
if (navigator.appVersion.indexOf("X11")!=-1) OSName="unix";
if (navigator.appVersion.indexOf("Linux")!=-1) OSName="linux";

return OSName;
}