Tag: Memory Hierarchy in Computer Architecture

Memory Hierarchy | Memory Hierarchy Diagram

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┬ácontained 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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