Same gpu with different memory size

Hi there, i have two Tesla M40 24G in my server, and i find two of them have different memory size, the bigger one contains 1.5GB more than the other, which seems not quite reasonable for me.


Could any one tell me what might cause it? thanks ahead.

ecc enabled on one, disabled on the other.
https://forums.developer.nvidia.com/t/a10-gpu-memory-was-only-22731m/199868/2?u=generix