System Summary reflects the overall performance and status of the system running Oracle DB from CPU and memory perspectives.

Number of CPUs – Total number of CPUs on the system

OS CPU Load - The percentage of CPU capability currently used by all System and User processes

CPU Usage: % of CPU busy (for all processes) and % of CPU busy for user processes

Total Physical Memory: Total memory on the system, one Instance in case of a RAC

Total Free Physical Memory: Total amount of free memory on the instance

System Physical Memory free: % of free physical memory