We assume that one has a system capable of effectively using its features:
Focus first on upgrading your system or acquiring a new system if it does not meet these minimums.
To use NaturallySpeaking Release 8, 256MB is minimum. It won't install with less. Period. The End. Don't even think about using less RAM.
You need at least 512MB if you are serious. Don't even think about complaining about performance or accuracy if you have less RAM than 512MB. If you have 512MB then you may be in good shape if you confine your computer usage to NaturallySpeaking plus one program like Outlook or Word. If buying a laptop that you expect to keep more than a year, get 1GB RAM if at all possible.
If you are serious about using NaturallySpeaking and time is important to you we recommend at least 1GB memory (RAM). If you normally use several programs or memory-intensive programs, more RAM may be useful.
At some point, adding RAM will not help. That will depend on your exact use of programs. Usually it is cheaper to add RAM than to pay someone to determine whether you need more or not. Or, try to monitor disk accesses while dictating. If you average less than one disk access per second while dictating, adding more RAM won't help you enough to bother.
RDRAM, DDR, etc. make a small difference compared to the amount of RAM. Consult the general trade press for information on the best type of RAM for your situation. Or just ignore it. NaturallySpeaking uses memory MUCH more than most other applications, so that memory plays a more important role in its performance than for most other programs. Don't be fooled by benchmarks with other application. If dealing with a local white box/clone builder, they will typically use one motherboard and one type of RAM for most of their systems. You will probably be better off going with their recommendation. If you don't like it, find a different system builder.
Watch out for cheap memory or for overclocking memory modules. Many a NaturallySpeaking problem has been solved by replacing memory. These problems are random and can be difficult to diagnose. But the problems are real, and even many of the conventional memory testing programs don't test memory as much as NaturallySpeaking. Just because "all my other programs work," do not assume that the memory on your system is in perfect working order.
Suggested supplier for additional RAM: Crucial.com