In Store Processor. In most multi-user POS system arrangements a central machine is used at the store level for PLU, IC, etc. This can be a server on a LAN, a central Unix workstation, a 4680 Controller, etc. Basically the individual POS terminals (or PCs) communicate with the ISP, which in turn communicates with the host, or back office system. Depending on the size of the retailer, the ISP can be the entire back office system.