In the Channel F, VRAM is a 128x64 pixel ( 8192 x 2 bits / 2kByte ) portion of RAM in the console, that can only be accessed through the ports. A portion of this VRAM is used as the display on the television screen. Column 125 and 126 controls the palette for the row of VRAM it is written on. The rest of the VRAM is unused by the console, but can be used to store data or be used as regular RAM by the game (however, Schach RAM is often better suited for use as RAM).
The portion of VRAM which is displayed starts at column 4, row 4 and expands 102 pixels horizontally and 58 pixels vertically, giving a resolution of 102x58 pixels. This resolution is used in the original release of the MESS emulation system. However, most televisions display a smaller resolution horizontally, so more accurately the resolution of the Channel F is about 95x58 pixels.
A screenshot from MESS displaying the visible and invisible portions of VRAM and the other shows screen of normal size in the same scale.