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2D and 2.5D Memory organization

  • Difficulty Level : Medium
  • Last Updated : 26 Feb, 2021

The internal structure of Memory either RAM or ROM is made up of memory cells that contain a memory bit. A group of 8 bits makes a byte. The memory is in the form of a multidimensional array of rows and columns. In which, each cell stores a bit and a complete row contains a word. A memory simply can be divided into this below form. 

2n = N

where,n is the no. of address lines and N is the total memory in bytes. 
There will be 2n words. 

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2D Memory organization – 
In 2D organization, memory is divided in the form of rows and columns(Matrix). Each row contains a word, now in this memory organization, there is a decoder. A decoder is a combinational circuit that contains n input lines and 2n output lines. One of the output lines selects the row by the address contained in the MAR and the word which is represented by that row gets selected and  is either read or written through the data lines. 


2.5D Memory organization – 
In 2.5D Organization the scenario is same but we have two different decoders one is column decoder and another is row decoder. Column decoder is used to select the column and row decoder is used to select the row. The address from the MAR goes as the decoders’ input. Decoders will select the respective cell through the bit outline,then the data from that location will be read or through the bit in line data will be written at that memory location. 


Read and Write Operations – 

  1. If the select line is in Read mode then the Word/bit which is represented by the MAR will be available to the data lines and will get read. 
  2. If the select line is in write mode then the data from memory data register (MDR) will be sent to the respective cell which is addressed by the memory address register (MAR). 
  3. With the help of the select line ,we can select the desired data and we can perform read and write operations on it. 

Comparison between 2D & 2.5D Organizations – 

  1. In 2D organization hardware is fixed but in 2.5D hardware changes. 
  2. 2D Organization requires more number of gates while 2.5D requires less. 
  3. 2D is more complex in comparison to the 2.5D organization. 
  4. Error correction is not possible in the 2D organization but in 2.5D it could be done easily. 
  5. 2D is more difficult to fabricate in comparison to the 2.5D organization. 


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