Why do we need transistor-based cache memory if random access memory, or RAM, is a memory that loses its contents when power is removed? Is there a limit to how much a computer's memory can store?

Due to the fact that both RAM (Random Access Memory) and volatile memory are transistor-based, it is not clear why cache memory is required. RAM (Random Access Memory) is already available as a volatile memory. Do you think that a computer could operate on a single kind of memory or on several types?

We already have RAM (Random Access Memory) as a volatile memory based on transistors, so why do we need cache memory? Do computers operate on a single kind of memory?

When we already have RAM, which is a volatile transistor-based memory, what is the use of cache memory? Is it feasible to use just one kind of computer memory?