understanding sdram geometry

Question

I am trying to understand the SDRAM and in the datasheet I am not able to understand the geometry. The SDRAM is a Samsung K4S561632N 32MB. http://www.samsung.com/global/business/semiconductor/product/consumer-dram/detail?productId=7147&iaId=742

In the datasheet http://www.samsung.com/global/business/semiconductor/file/2011/product/2010/5/6/135616ds_k4s56xx32n_rev10.pdf it is given that "The K4S560432N / K4S560832N / K4S561632N is 268,435,456 bits synchronous high data rate Dynamic RAM organized as 4 x 16,777,216 words by 4 bits / 4 x 8,388,608 words by 8bits / 4 x 4,194,304 words by 16bits, fabricated with SAMSUNG's high performance CMOS technology."

The last numbers i.e. 4x4,194,304 words by 16bits I am able to understand that the first number is bank. I am not able to understand the second and third numbers. What does a 'word' mean there (1 byte or 2 bytes??)? Is it the number of rows by columns?

Answer 1

The "by 4 bits/by 8 bits/..." gives the word size - there are twice as many words in the 8 bit per word mode as there are in the 16 bit per word mode.

Answer 2

Please read this and this to learn more about the SDRAM's structure. "Word" in SDRAM is the minimum memory unit which can be addressed.