After you purchase a host license, VMware provides a serial number that you can use to license vSphere. You can use evaluation mode to access the full ESXi feature set, including features you have not purchased a license for.

For example, in evaluation mode, you can use vMotion, HA, DRS, and other features, even if you have not licensed those features.

The installable version of ESXi is always installed in evaluation mode. ESXi Embedded is preinstalled on an internal USB device by your hardware vendor. It might be in evaluation mode or prelicensed.

The evaluation period is 60 days and begins when you turn on the ESXi host, even if you start in licensed mode rather than evaluation mode. Any time during the 60-day evaluation period, you can convert from licensed mode to evaluation mode. To take full advantage of the 60-day evaluation period, you should convert to evaluation mode as soon as possible after you first power on the host. See Convert an ESXi Host to Evaluation Mode.

For information about licensing the host, see the vCenter Server and Host Management.