Method and apparatus for providing modular I/O expansion of computing devices

An apparatus comprising:

• a host computing device having a host port, said host computing device comprising:
• at least one port interface object accessible by at least one application executing within said host computing device;
• a first multiplexor coupled to said at least one port interface object and said host port, said first multiplexor comprising a current first routing state specifying a flow of data between said at least one port interface object and said host port, said first multiplexor configured to change said current first routing state in response to a control signal received from said host port;
• an expansion unit having a main port linked to said host port, said expansion unit comprising:
• at least one port interface module configured to couple at least one device to said expansion unit;
• and
• a second multiplexor coupled to said at least one port interface module and said main port, said second multiplexor comprising a current second routing state specifying a flow of data between said at least one port interface module and said main port, said second multiplexor configured to change said second current routing state in response to a control signal received from said main port.