IBM had at least two computers that used this concept: The PCJr, and the IBM Convertible "laptop".
One of the many problems with sidecars is that they make the computer footprint larger. While it hypothetically allows for unlimited expansion compared to a limited number of internal slots, this would be practically limited by physical space and electrical signaling issues.
One of the many problems with sidecars is that they make the computer footprint larger. While it hypothetically allows for unlimited expansion compared to a limited number of internal slots, this would be practically limited by physical space and electrical signaling issues.