The PXI Carrier Module for SwitchBlock can hold up to six Matrix Modules for SwitchBlock while occupying four PXI slots. By connecting multiple SwitchBlock relay cards through the carrier's integrated analog bus, you can easily create large matrices with more than 2,000 crosspoints in four PXI slots and more than 8,000 crosspoints in a single PXI chassis. Each Matrix Module for SwitchBlock comes in an A-type version, which serves as the first matrix building block and offers row and column access through the front connector, and a B-type version, which serves as an expansion module and only provides column access through the front connector. Typically, SwitchBlock systems contain one A-type module and numerous B-type modules.