Purpose of storage:
Several different forms of storage, based on different natural phenomena, have been invented. So far, no practical universal storage medium persists, and all forms of storage have some disadvantage. So a computer system typically contains many kinds of storage, each with an specific purpose.
A digital computer represents data by using the binary numeral system. Numbers, Text, audio, pictures and nearly any other form of information can be transformed into a string of bits/ binary digits, each of which has a value of 0 or 1. The most general unit of storage is the byte that is equal to 8 bits. A piece of information can be handled by any computer whose storage space is big enough to accommodate the binary representation of the piece of information, or simply data. For instance, by using 8 million bits, or approximate 1 megabyte, a typical computer could store a short novel.
Traditionally the most essential part of every computer is the central processing unit (CPU, or simply a processor), because it in fact operates on data, performs any calculations, and controls all the other components.
In practice, mostly all computers use a variety of memory types that organized in a storage hierarchy around the CPU, as a tradeoff amongst cost and performance. Usually, the lower a storage is in the hierarchy, lesser its bandwidth and the greater its access latency is from the CPU. This usual division of storage to, secondary, tertiary, primary and off-line storage is also guided by cost per bit.