MEMORY HIERARCHY

• Today's computer systems use a combination of memory types to provide the best performance at the best cost . This approach is called Hierarchical memory.
• The basic types that normally constitute the hierarchical memory system includes Registers , Cache ,Main memory, and Secondary memory.
• The memory unit that communicates directly with the CPU is called the Main memory. Devices that provide backup storage are called Auxiliary memory.
• We classify memory based on its “distance” from the processor. The closer memory is to the processor, the faster is its working.

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• Magnetic disk and tapes are auxiliary memory .They are used for storing system programs, large data files , and other backup information.
• They are connected to main memory with help of I/O processor
• Only programs and data currently needed by the processor reside in main memory .
• All other information is stored in auxiliary memory and transferred to main memory when needed.
• Both main memory and cache are connected to CPU directly.

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• A special very-high-speed memory called a Cache is used to increase the speed of processing by making current programs and data available to the CPU at a rapid rate.

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• The cache is used for storing segments of programs currently being executed in the CPU and temporary data frequently needed in the present calculations.

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• Multiprogramming:�It refers to the existence of two or more programs in different parts of memory hierarchy at the same time.��

MEMORY HIERARCHY

Increase in

• Cost per Bit
• Speed
• Transfer Rate

Decrease in size.

Increase in

• Storing capacity
• Transfer Time
• Access time

Advantages of memory hierarchy:�����

• Decrease frequency of accesses to slow memory.
• Decrease cost/bit.
• Improve average access time.
• Increase capacity�

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