A computer device comprises a processor for executing a plurality of concurrent processes each comprising a sequence of instructions, memory including RAM, at least one message link having input and output pins for connection to a device separate from said computer device and for transmitting message packets sequentially between the computer device and said separate device, and communication control circuitry coupled to said processor, to said memory, and to said message link. The memory provides a plurality of addressable virtual communication links. The communication control circuitry is operable: (i) in response to execution of a message instruction by said processor to address a selected one of said virtual communication links and load into the selected one information regarding the message to be effected via the virtual communication link; and (ii) to control sequential transmission through said one message link of message packets relating to a plurality of virtual communication links. A network of such computer devices and a method of operation is also described. The provision of virtual links enables several messages to be multiplexed down a single message link of the microcomputer.