A system and methods of uploading payload data to user buffers in system memory and of uploading partially processed frame data to legacy buffers allocated in Operating System memory space are described. User buffers are stored in a portion of system memory allocated to an application program, therefore data stored in user buffers does not need to be copied from another portion of system memory to the portion of system memory allocated to the application program. When partially processed frame data is uploaded by hardware to a legacy buffer in system memory, a tag, uniquely identifying the legacy buffer location is transferred by the hardware to a TCP stack, enabling the TCP stack to locate the legacy buffer.