C4 and C5a are Amazon Web Services (AWS) "Instance Types: https://aws.amazon.com/ec2/instance-types/ C4 is a virtual server with the Intel Xeon E5-2666 v3 (Haswell) processor, running at about 2.9 GHz C5a is a virtual server with the AMD EPYC 7002 series processors running at frequencies up to 3.3 GHz Lewis