1. An apparatus for virtual desktop service, comprising: a processor to perform an assignment task of assigning a virtual machine to a user terminal using the virtual desktop service, wherein software resources including an operating system, applications, and user profiles ace provided to the virtual desktop service, and wherein hardware resources are supported for the virtual desktop service, wherein the processor performs a delivery function for a delivery protocol, and the delivery function provides a communication channel between the apparatus and the user terminal; wherein the delivery function determines a connection result based on environmental parameters for the virtual desktop service received from the user terminal, wherein the environmental parameters include a screen resolution, a compression rate of video and audio, and a kind of video and audio codec, wherein the processor further performs connection management function, wherein the connection management function identifies a first type of user, a second type of user or a third type of user from the user terminal, wherein the processor persistently allocates a permanent virtual machine by adopting a pre-set method and a manual method to the first type of user, wherein the processor allocates a non-persistent virtual machine for one time use to the second type of user, wherein when an access of the second type of user is released, a personal profile of the second type of user is not stored, and wherein the processor allocates multiple virtual machines to the third type of user.