 Because of the standard's genesis in the VME world it is sized such that 4 fit in a 6U module and 2 in a 3U module.Conveniently, because of the way other backplane standards have evolved, 4 units easily fit the front panel space in VXI and 6U cPCI/PXI while 2 will fit in the front panel space of 3U cPCI/PXI and up to 8 will fit in a 1U LXI rack mount carrier.At the present time a number of instruments are available in the M-Module form factor in the following categories