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RS-232 is an old standard originally conceived for serial data communication between a modem and a computer or computer terminal, normally using DB-9 or DB-25 connectors. It was embodied in the COM ports that were once a feature of virtually all personal and home computers. Although now superseded by USB, due to its great simplicity and former ubiquity it is still used where low speed communication is required over a limited distance. RS-422 and RS-485 are later variants offering enhance speed, maximum distance or connnectivity options.