(1) (Main Distribution Frame) A wiring rack that connects outside lines with internal lines. It is used to connect public or private lines coming into the building to internal networks. In a telco central office (CO), the MDF is generally in close proximity to the telephone switch. See IDF, CDF and wiring rack.

(2) (Multiple Domain Facility) Hardware and microcode supplied by Amdahl that allows the running of multiple system images on a single processor complex. MDF was the first such implementation that did not depend on software such as VM/370 or VM/ESA.