swap disk = slow memory for your system
ram disk = fast disk space
you can easily spare lots of swap space from your drive, if you have several gigs, and it can greatly help your system to have your swap disk seperated from the rest of your disk by making a seperate partition. it improves performance of your system greatly. and it is a cheap price.
ram disk is much more expensive. you don t get much storage space, ram space is much much more expensive than disk space, and every meg of ram that you use for disk space costs you RAM you could use for memory which will slow your system. but if you have lots of ram to spare, and you can afford it, then you get a disk that is extremely extremely fast. for things like web caching, it can be really effective, if you can spare the ram. a lot of people really like this feature.
according to the darwin developer who posted on the thread i put up before, implementing an efficient ram disk is extremely difficult. so you hear it from the horses mouth. RAM disk is not available in OSX. i personally believe that apple will want to offer us at least every feature for OSX that was available for OS9, so i think it will come out eventually for OSX, though i don t think it will be soon. i don t personally have a use for RAM disk, ut it sounds cool, and i can imagine that when i need it, it will come in great use.
let s be patient, shall we?