A Class I Core(AKA a Central-Class Core) is, put simply, GLaDOS. There is no other information, because there is only one.(unless you count the multiple GLaDOS') Class I cores have a normal information capacity of several zettabytes, and an emotional information capacity of 100,000,000 units. They have a control capacity of a quadrillion units.
List of Cores
GLaDOS
GLaDOS 2.0