2D and 2.5D Memory organization



Internal structure of Memory either RAM or ROM is made of memory cells which contains a memory bit. Basically group of 8 bits makes a word. Now the memory is formed in 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 in 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.

2D Memory organization –
Basically in 2D organization memory is divides in the form of rows and columns. Each row contains a word now in this memory organization there is a decoder. A decoder is a combinational circuit which contains n input lines and 2n output lines. One of the output line will select the row which address is contained in the MAR. And the word which is represented by the row that will get selected and either read or write through the data lines.

2.5D Memory organization –
In 2.5D Organization the scenario is the same but we have two different decoders one is column decoder and another is row decoder. Column decoder used to select the column and row decoder is used to select the column. Address from the MAR will go in decoders’ input. Decoders will select the respective cell. Through the bit outline, 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 that will be coming out to the data lines and get read.
  2. If the select line is in write mode then the data from memory data register (MDR) will go to the respective cell which is addressed by the memory address register (MAR).
  3. With the help of the select line the data will get selected where the read and write operations will take place.

Comparison between 2D & 2.5D Organizations –

  1. In 2D organization hardware is fixed but in 2.5D hardware changes.
  2. 2D Organization requires more no. of Gates while 2.5D requires less no. of Gates.
  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 error correction is easy.
  5. 2D is more difficult to fabricate in comparison to the 2.5D organization.


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