I have DB RCFS version 4.0 - 4.6, version 5.0 and 2001. There is not a lot of difference between 4.0 and 5.0 except that the flight physics are a lot better and there is some improvement in the graphics. All the versions through 5.0 are vector graphics which are far less CPU intensive than the 3D graphics of today. Even version 5.0 will run on a 386 based machine. The simulator, although primitive in appearance, will give you hours of useful stick time when it is dark or raining.