First VM is created on VMware the second VM is on Oracle Virtual Server 3.1.1.
The VMware server is on the same HW architecture as Oracle VM Server (two blade as twins).
I've created Oracle database server 11gR2 on both VM.
The Enterprise Manager Cloud Control "Database - Performance Home" page shows 4 CPU Cores in case of VMware VM,
but only 1 CPU Core in case of Oracle VM.
Did you set processors and the max processors the same on the VM guests?
One CPU is one CPU core. If you do not use CPU pinning..... CPU core allocation is load balanced across all cores in the system. When you use CPU pinning. (Which you must do in a oracle database to adhere to licensing requirements where they apply) CPU cores are dedicated to the VM guest and not load balanced. You can overcommit CPU resources in Oracle VM. In other words. You can set max CPU across all VM guests on a single VM server to be greater than the total amount of CPU cores available in the system. Check out article 464754.1