How to tell which is which.

Before the last big round of updates, there was a distinct difference between an update and an insider preview. Trouble is, I have one machine with both on, hardware switched. They both say 10586.11 at present, although I thought they were at 10586.3. Any mention of "insider" has vanished, as has "fast track". I thought that I had fitted the 240gb ssd to the upgrade and was running the preview on a smaller drive, but I'm not sure any more.

There is no current insider build of Windows 10. You can look under the advanced options section of the Windows Update control panel and see if that installation of Windows 10 is enrolled in the insider program to get future insider builds.

Thanks, I have got the ssd running the correct version. Sooner or later I will retire the ex preview one as even if Microsoft ends up donating them to insiders, it won't do me any good.