VMRs in general
For each voxel of a VMR an unsigned char (1 byte) is stored. If a corresponding V16 (16-bit precision) file is loaded as well, a total of 3 bytes per voxel is occupied by the data.
1mm VMRs
In their native voxel matrix size (256 x 256 x 256), each VMR uses approx. 16MB of RAM.
0.5mm VMRs
Doubling the resolution in each spatial dimension requires 8 times the memory, i.e. 128MB for a fullsize matrix. BrainVoyager gives you the opportunity to remove all non-head portions of the image, so to usually save roughly 70 per cent of the space leading to roughly 35MB to 40MB.