This post will cover techniques that can be used to detect virtualized environment. This techniques uses special I/O port to send command and get output. In above image, VMWare I-O port is command number 0x0A (get vmware version)VMware version is return in register EAX as shown below. If value in register is 0 which means Virtual PC detected. If opcode is run outside Virtual PC, illegal instruction exception is thrown otherwise return value inregister is checked.”]
Source: https://shasaurabh.blogspot.com/2017/07/virtual-machine-detection-techniques.html