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Explanation: Many computer firms prefer to make a distinction between the peripheral cards or boards (tarjetas) and the main board (placa de sistema, placa matriz, or even "motherboard" carried over from English). Generally, the latter is larger and is attached to the computer's chassis. The smaller "boards" or "cards" are inserted into slots as add-ons. So, in your example I would recommend "tarjetas" for the detector preamplifier boards, but "sistema de computadora (OR ordenador for Spain) de placa única" when referring to the single-board computer system.