Virtual Disk Development Kit FAQ

VI API is a Web Service and XML interface focused on management of virtual machines and ESX server configuration.

VCB offers command-line tools to integrate with backup products on SAN.

The VDDK is focused on efficient access and transfer of data on virtual disk storage. The VDDK can be used in conjunction with other APIs to offer a complete integrated solution for management of virtual infrastructure.

via Virtual Disk Development Kit FAQ.