Why isn't RAM as fast as registers/cache memory? [closed]

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Why do we need to cache in Cache Memory? Why cant RAM Memory be made as fast as register or Cache Memory or Cache be as 开发者_开发百科large as RAM Memory (4GB) so that everything can be in cache? Any good article/books to understand these concepts?

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Faster stuff costs more per bit. So you have a descending chain of storage, from a few registers at one end, through several levels of cache, down to RAM. Each level is bigger and slower than the one before. And all the way at the bottom you have disk.

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Registers and cache are on the cpu chip itself, or tied to it very closely. Normal RAM is accessed through an address bus, and it often subject to a level of indirection by memory mapping.