Data Storage.

Data Storage.


Without a memory no information can be stored or retrieved in a computer. Computer memory has experienced a similar increase along a different dimension. While processing speed increases at the same rate that memory size increases, the gap between the speed of the processor and the speed of memory also increases.
As the gap between processor and memory speeds grows, architectural solutions help bridge the gap. A typical computer contains several types of memory, ranging from fast, expensive internal registers, to slow, inexpensive removable disks. The interplay between these different types of memory is exploited so that a computer behaves as if it has a single, large, fast memory, when in fact it contains a range of memory types that operate in a highly coordinated fashion.

13-Memory Hierarchy
Memory in a conventional digital computer is organized in a hierarchy as illustrated in Figure 7. At the top of the hierarchy are registers that are matched in speed to the CPU, but tend to be large and consume a significant amount of power. There are normally only a small number of registers in a processor, on the order of a few hundred or less. At the bottom of the hierarchy are secondary and off-line storage memories such as hard magnetic disks and magnetic tapes, in which the cost per stored bit is small in terms of money and electrical power, but the access time is very long when compared with registers. Between the registers and secondary storage are a number of other forms of memory that bridge the gap between the two.