This illustration shows three instances, instances X, Y, and Z, accessing data files. The instances are all conneted to an interconnect that they use for internode communication.
Within each node there are the following structures: the variable part of the System Global Area (SGA), a redo log buffer, and a database buffer cache. The Diagnostic process (DIAG) also appears within each instance.
The variable SGA launches the following sub-processes: LMON, LMD, and LCK.
The Interprocess Communication (IPC) connects the LMON of each instance to each other.
The redo log buffer writes to the Log Writer Process (LGWR) which writes to the redo logs. The Database Buffer Cache writes to the Database Writer process (DBWR) which writes to the shared disks. The Database Buffer Cache also writes to the Global Cache Service (LMSn) processes.