Retroarch: what the "memory" counter means?

When i use Retroarch with Direct X 11 or 12 drivers, i get a “Memory” counter like 1500/4095. Its clear to me, this is a ram counter, the 4000 is the total ram in my system, but what the FIRST number means? a- Free memory? b- memory used by Retroarch? c- memory used by all process in my pc?

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