1. A system comprising: a virtual execution environment; a block granularity caching engine; a cache; wherein, in operation: a process associated with a stream-enabled application is executed in the virtual execution environment; the virtual execution environment intercepts a request for a resource from the process executing in the virtual execution environment; the virtual execution environment identifies one or more blocks that are associated with the resource; the virtual execution environment makes a block request associated with the resource; the block granularity engine checks the cache for blocks to satisfy the block request; the block granularity caching engine provides at least one predictively streamed block to the virtual execution environment if the predictively streamed block is found in the cache, the predictively streamed block included as part of an output buffer having a buffer length dependent on a data window size based on an interactivity threshold of the stream-enabled application, the interactivity threshold being an amount of time that a user is willing to wait for the virtual execution environment to access the resource and based on an average user response that is determined by executing the process in the virtual execution environment multiple times, receiving a plurality of user responses to the execution process and averaging the plurality of user responses to create the average user response; the virtual execution environment satisfies the resource request of the process using the at least one predictively streamed block.