Stands for "Sequenced Packet Exchange." SPX is networking protocol primarily used by Novell Netware, but is also supported by other operating systems. It is now considered a legacy protocol since it has largely been replaced by TCP/IP.
SPX is the transport layer of the the IPX/SPX protocol and IPX is the network layer. SPX handles the connections between systems while IPXhandles the actual transfer of data. Therefore, SPX commands are used to establish, confirm, and close connections, while IPX commands are used to send and receive data packets. SPX is similar to TCP and IPX is similar to IP in the TCP/IP protocol.
The IPX/SPX (or SPX/IPX) protocol originally handled the transport and network commands for the NetWare Core Protocol (NCP). A system running NCP Server (typically a Linux machine) could receive connections from computers running NCP client software. The NCP protocol provided functions for accessing files and directories, syncing clocks, and messaging between systems. When Novell enabled NCP servers to use the universal TCP/IP protocol, it soon replaced the proprietary NCP protocol suite.
NOTE: Micro Focus acquired Novell in November, 2014.