1. A segmented virtual machine (VM) executing within one or more computer systems, the segmented virtual machine comprising: a plurality of core VM's implemented in a common core space; and a plurality of shell VM's each associated with a core VM; wherein: the plurality of core VM's each perform VM internal execution functions; the plurality of shell VM's each perform interactions with an external environment and are configured to forward certain calls from the external environment to its associated core VM; the plurality of core VM's and the plurality of shell VM's cooperate to form the segmented VM; and resources of the common core space are allocated among the core VM's according to a policy indicating resource requirement of the plurality of core VM's, the resource requirement including priority information pertaining to each of the plurality of core VM's.