Raster:memory or disk?

Hi!

Is there any way to check if the values of a raster object
are in memory or in disk?

For example
r10 <- raster("2000_TSDP_IP-INVDIST-SP10_43023435.tif")
b <- r10

I understand that values of r10 are not loaded in memory
but b is completely in memory (am I wrong?)
How could I actually verify this?

Thanks

Agus