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Virtual memory (transferring from physical RAM to the hard disk) theoretically allows processes to take as much memory as they want (within the limit of the hard disk obviously).

However, since disk access is many orders of magnitude slower than RAM access, the more of the process can live in RAM the better.

Also, virtual memory only really works well as long as there is a pattern to data access. If things keep having to get written out to disk after every access (because they are not in RAM) then performance is catastrophic. For example, doing a naive sort of a large data set will perform very badly (you'd need to use an external merge sort or something similar).

Virtual Memory technology allows process announce RAMs larger than real RAM size, and put recently used block in real memory, others in disk. when load a not-in-ram block, it would do paging, means kick out a loaded block and load target block in real memory.

Larger RAM allows more blocks loaded in real RAM, that is, larger ram will lower page rate, and that would save much time.