Abstract: A modular plug-in instrumentation system for enabling a personal computer to perform instrumentation functions, including receiving analog and digital signals from an external device and transmitting analog and digital signals to an external device, includes a carrier module pluggable into a bus of the personal computer, and also includes an internal instrumentation bus into which a plurality of different interchangeable instrument modules can be plugged. The instrumentation bus includes a digital portion, and also includes a segmented analog portion that is extendable merely by plugging instrumentation modules into bus connectors which span gaps between the analog bus segments. Analog and/or digital signals are communicated between various instrument modules and external devices by means of cables connected to the instrument modules.