Thanks very much to Hadron and Chanchan05 for their help. My interest in OS on phones is very recent and my paradigm is that of my PC. I bought my PC from Dell and it came with the OS installed but if I want an upgrade to the OS I go, not to Dell, but (in my case) to Microsoft who write the software. I infer from what you say that although the ultimate source of Android is Google, no end users get their OS sofware from Google but from the manufacturers of their handsets. I understand that the "No update available" message came from my phone but was the phone not just passing on to me information obtained from the server (Samsung, in my case?) vis. that there was no update available?