Matrox CronosPlus Installation And Hardware Reference page 19

Grabbing simultaneously from different boards 19
problems when grabbing up to two full-sized color images simultaneously (using
two boards). However, grabbing more than two full-sized color images
simultaneously might result in PCI bandwidth problems.
As a reference point, grabbing one full-sized NTSC or PAL image in real time will
require a PCI bandwidth of 35 Mbytes/sec or 42 Mbytes/sec, respectively, when
transferring in RGBX (32-bit) mode.
When grabbing from three or more Matrox CronosPlus boards simultaneously,
you will have to reduce the image size to avoid reaching the upper limits of the
overall available bandwidth.