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Nexys A7 100T - on board memory spec question



In section 3 of the user manual for my Nexys A7 FPGA development board there is the following statement regarding the 2 external memories...

"1Gib (128MiB) DDR2 SDRAM and a 128Mib (16MiB) non-volatile serial Flash device"

I don't completely understand the specs in parenthesis? I think they may refer to configurations within the memory ICs themselves. 

For instance... for the DDR2 SDRAM, PN: MT47H64M16HR-25E I looked at the data sheet and saw the following configuration option listed...

128 Meg x 8 (16 Meg x 8 x 8 banks) 

So I just wanted to try and better understand these specs for the on board memory. 

thank you



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Yeah, that's really confusing isn't it?

At issue is the fact that many of these chips are specified in Mega BITS not BYTES.  So the 1Gib is mean to refer to a one gigabit memory, which is also a 128 megabyte memory.  That's what the parentheses are trying to tell you.

Where this becomes a real problem is that I've always learned that a MiB is a reference to a million bytes, 10^6 bytes, rather than a mega byte, or 2^20 bytes.  The proper acronyms, IMHO, should be Gb, GB, Mb, and MB rather than GiB or MiB which are entirely misleading.

As for the memory, listed as 16 Meg x 8 x 8, that's a reference to 8-banks of 16-mega words or memory, where each word is 8-bits wide.  In other words, the memory has 16MB*8 or 128MB of storage.  You could alternatively say it had 1Gb of memory, which would be the same thing, but this is often confused with 1GB of memory--hence the desire for the parentheses again.


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