A server system has, in addition to extensibility of scale-out type of a braid server system, extensibility of scaleup type by making SMP coupling among nodes. Each node has a unit for SMP coupling to other nodes and a module management unit of each node responds to system configuration information to switch between mode in which the node operates singularly as a braid server and mode in which the node operates as a constituent module of an SMP server. Links among individual nodes are laid through equidistant wiring lines on a back plane and besides a loop wiring line having length equal to that of the inter-node link on back plane is also laid in each node, thereby setting up synchronization among nodes. Each node has a reference clock distribution unit mounted on back plane and adapted to distribute reference clocks to individual nodes and by switching reference clocks by a clock distributor inside each node, synchronization of reference clocks for SMP coupled nodes can be established.