A gateway for use in a computing system to interface a host with the subsystem for acting as a work accelerator to the host, the gateway having an streaming engine for controlling the streaming of batches of data into and out of the gateway in response to pre-compiled data exchange synchronisation points attained by the subsystem, wherein the streaming of batches of data is selectively via at least one of an accelerator interface, a data connection interface, a gateway interface and an memory interface, wherein the streaming engine is configured to perform data preparation processing of the batches of data streamed into the gateway prior to said batches of data being streamed out of the gateway, wherein the data preparation processing comprises at least one of: data augmentation; decompression; and decryption.