Why does the guest operating system report that it is connected at 10Mbps while the ESX host has a 100Mbps or 1000Mbps network adapter?

VMware GSX Server 3.x (Linux)
VMware Workstation 7.x (Windows)
VMware Workstation 6.x (Linux)
VMware ESX Server 2.1.x
VMware vSphere ESXi 5.0
VMware Workstation 4.x (Windows)
VMware ESXi 4.1.x Installable
VMware GSX Server 2.x (Linux)
VMware ESX Server 2.0.x
VMware ESX Server 2.5.x
VMware ESX Server 3.5.x
VMware ESX 4.1.x
VMware Workstation 3.x (Linux)
VMware Workstation 11.x (for Windows)
VMware ESXi 4.0.x Installable
VMware Workstation 3.x (Windows)
VMware vSphere ESXi 5.5
VMware ESXi 3.5.x Embedded
VMware GSX Server 2.x (Windows)
VMware Workstation 7.x (Linux)
VMware ESXi 4.0.x Embedded
VMware ESXi 3.5.x Installable
VMware vSphere ESXi 5.1
VMware Workstation 4.x (Linux)
VMware Workstation 11.x (for Linux)
VMware Workstation 10.x (Linux)
VMware ESX Server 1.x
VMware ESX Server 3.0.x
VMware GSX Server 3.x (Windows)
VMware Workstation 9.x (Linux)
VMware Workstation 8.x (Windows)
VMware ESX Server 1.5.x
VMware Workstation 10.x (Windows)
VMware Workstation 9.x (Windows)
VMware ESX 4.0.x
VMware Workstation 5.x (Windows)
VMware ESXi 4.1.x Embedded
VMware Workstation 5.x (Linux)
VMware Workstation 6.x (Windows)
VMware Workstation 8.x (Linux)

The network adapter speed reported by the guest operating system is not representative of the actual speed of the physical network connection.

The guest operating system passes data packets as fast as it can based on the host CPU load and the physical Ethernet bandwidth of the host, so one may ignore the LAN connection speed reported by the guest operating system.

To verify this, use FTP or SMB in the guest operating system to transfer a file. Check the transfer rate, which should show that the virtual network adapter is not limited to the 10Mbps limit reported in the guest operating system, as the external network is faster than 10Mbps.

The guest operating system reports the 10Mbps speed because the virtual network adapter is an AMD PCnet II compatible NIC, which by definition is a 10Mbps NIC.

Even though the virtual NIC identifies as 10Mbps, it actually runs at the higher rate of the NIC within the ESX host.