The main difference is that RAM is volatile and flash is non-volatile, meaning that flash memory will store data without being supplied with power. RAM will not retain data without power. So they have different functions and are used for different things.

A flash drive is a storage device that uses flash memory rather than conventional spinning platters to store data. Random access memory (RAM) is a type of computer data storage. Today it takes the form of integrated circuits that allow the stored data to be accessed in any order, i.e. at random. The word random thus refers to the fact that any piece of data can be returned in a constant time, regardless of its physical location and whether or not it is related to the previous piece of data

Technically speaking, RAM (random access memory) is any medium of storing information electronically so it can be accessed in a random sequence. This means some things we don't normally call RAM are also RAM. Hard drives, floppy discs, CD/DVD drives are all examples of data storage we don't generally refer to as RAM. However, they have identical characteristics. The term RAM for electronic memory came at a time when mechanical mediums of data storage had such constraints as to require information to be recovered in a specific sequence. RAM was a revolutionary development in computing. It could be compared to the difference between a VCR and DVD player. The video cassette tape is strictly sequential in the order it could recover data. In this case, recover data means watch your recorded show. You had to queue it up to the spot (past the commercials) where you wanted to start viewing. Part of the beauty of DVD is that it can access information from the disc in just about any order, just like RAM. When the current generation of kids grows up, you'd have to explain to them the limitations of the VCR before the true beauty of the DVD's ability to access information at any sequence becomes apparent. Hope it helps you.

Flash memory is Non volatile and RAM is Volatile memory..