Main memory is large, inexpensive, slow memory stores entire program and data.
Cache memory is small, expensive, fast memory stores copy of likely accessed parts of large memory.
There are four major storage levels.
1.Internal-Processor, register, and cache.
2.Main-the system RAM and controller cards.
3.On-line mass storage-secondary storage.
4.Off-line bulk storage-tertiary and off-line storage.
Memory or storage are classified into two categories:
In memory hierarchy the smaller memory is faster and larger memory storage is slower.