It insulates all clients from the database layer below. This server cooperates with all channel access clients to implement the callback and synchronization mechanisms already described. A channel is a path to one or more attributes of a record in the database. The record name and attribute is the only way that CA connects a client to a server. Records sup- port a great variety of data linkage and flow control, such as sequential, parallel, and conditional.
Data can flow from the hardware level up, or from the software level down.
Although all record parameters are generated with a configuration tool on a workstation, most can be dynamically updated by channel access clients, but with full data independence. This is one of the few places where new C code often appears. Linkages between records are not restricted to one IOC, but can span multiple IOCs. The fifth, bottom layer of software is the device driver layer. A large and rapidly growing list of drivers has been written for many popular VME and VXI interface boards, serial devices, and Industry Packs.