Memory Hierarchy-

 

• Memory hierarchy is the hierarchy of memory and storage devices found in a computer system.
• It ranges from the slowest but high capacity auxiliary memory to the fastest but low capacity cache memory.

 

Need-

 

There is a trade-off among the three key characteristics of memory namely-

• Cost
• Capacity
• Access time

Memory hierarchy is employed to balance this trade-off.

 

Memory Hierarchy Diagram-

 

 

Level-0:

 

• At level-0, registers are present which are contained inside the CPU.
• Since they are present inside the CPU, they have least access time.
• They are most expensive and therefore smallest in size (in KB).
• Registers are implemented using Flip-Flops.

 

Level-1:

 

• At level-1, Cache Memory is present.
• It stores the segments of program that are frequently accessed by the processor.
• It is expensive and therefore smaller in size (in MB).
• Cache memory is implemented using static RAM.

 

Level-2:

 

• At level-2, main memory is present.
• It can communicate directly with the CPU and with auxiliary memory devices through an I/O processor.
• It is less expensive than cache memory and therefore larger in size (in few GB).
• Main memory is implemented using dynamic RAM.

 

Level-3:

 

• At level-3, secondary storage devices like Magnetic Disk are present.
• They are used as back up storage.
• They are cheaper than main memory and therefore much larger in size (in few TB).

 

Level-4:

 

• At level-4, tertiary storage devices like magnetic tape are present.
• They are used to store removable files.
• They are cheapest and largest in size (1-20 TB).

 

Observations-

 

The following observations can be made when going down in the memory hierarchy-

• Cost / bit decreases
• Frequency of access decreases
• Capacity increases
• Access time increases

 

Goals of Memory Hierarchy-

 

The goals of memory hierarchy are-

• To obtain the highest possible average access speed
• To minimize the total cost of the entire memory system

 

To gain better understanding about Memory Hierarchy-

Watch this Video Lecture

 

Next Article- Memory Organization | Simultaneous Vs Hierarchical

 

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