How to calculate SDRAM capacity

When I was reading the chip manual of SDRAM, I kept thinking about this question: How is the capacity of SDRAM calculated? After searching various materials on the Internet, I finally share my summary with you!

Take the model of the SDRAM chip manual of my development board: h57v2562gtr60c as an example. By looking at the datasheet of my h57v2562gtr60c, we know that

there are 13 row address selection lines (RA0~RA12), 9 column address selection lines (CA0~CA8), 
2 bank selection lines (BA0, BA1), and 16 data lines (DQ0~AQ15).

We know that the total number of SDRAM cells = (2^row address selection lines) * (2^column address selection lines) * (2^Bank selection lines).

From this, we can conclude that the total number of our SDRAM cells = (2^13)*(2^9)*(2^2)=2^24 cells.

Note: The row address selection line bit 13 does not mean that each of our banks has only 13 rows, but that the number of rows that can be represented by each bank is 2^13 rows. The same is true for the column address selection lines and bank lines.

We know the total number of SDRAM cells, but we cannot determine the capacity of the entire SDRAM, because we do not know how many bits of data are stored in each cell of our SDRAM. So how is this determined?

Then this involves the concept of bit width. In the TQ2440 development board, two SDRAMs are used to form a whole SDRAM, in which the address line shares the same address, and the data line is divided into two 16-bit, because each SDRAM only provides 16 data lines, so my personal understanding is: the lower 16 bits exist in one of the SDRAMs, and the upper 16 bits exist in the other SDRAM, so that every time data is sent or read to the same address, the purpose of sending or reading 32-bit wide data is achieved, that is, the data of a storage unit corresponding to each address is 32 bits.

So the capacity of our entire SDRAM = (total number of SDRAM units) * (bit width) = (2^24) * 32 = 2^29 bit

Note: I am calculating the total capacity of the entire SDRAM of the TQ2440 development board, not the total capacity of each individual SDRAM. If the capacity of each SDRAM chip = the capacity of the entire SDRAM / 2 

Note: The unit of calculation here is bit. If we convert it into bytes, it is 2^29 bit / 8 = 2^26 Byte = 2^6 MB = 64 MB

This is the final SDRAM capacity of the TQ2440 development board.