Upgrade of software images based on streaming technique

Migrating a data-processing entity from a source software image installed on a mass memory of the data-processing entity to a target software image stored on an external source. A portion of mass memory is released. Memory blocks stored in boot locations of the target software image are relocated to the released portion, including memory blocks required to boot the data-processing entity to load a streaming function for downloading the target software image from the external source. The data-processing entity is booted from the boot blocks, thereby loading the streaming function. Each request for reading a selected memory block of the target software image is served by the streaming function, which downloads the selected memory block from the external source and stores it into the released portion when the selected memory block is not available in the mass memory, or retrieves the selected memory block from the mass memory.