Hardware Compatibility: the VL/PCI Bus and the Graphics Board The functionality of a graphics system depends mainly on two components: the graphics board and the mainboard. If either the design of the VL bus or the PCI mainboard is not compliant with the approved VESA or PCI specifications you may experience problems with the graphics board. SPEA has successfully tested the SPEA VL bus graphics boards in VL bus mainboard with a clock rate of 40 MHz and PCI bus mainboards with a clock rate of 66 Mhz.