While lists are available to show you what platforms are affected by Spectre and Meltdown, it'd be nice if you could just run a tool and have it tell you what you're protected against. For Windows users, SpecuCheck is one such option.
A few caveats. Firstly, you'll have to make sure your Windows install is up-to-date, as the utility relies on new API calls to gather the information it needs, specifically
NtQuerySystemInformation. Secondly, Ionescu recommends using Microsoft's own PowerShell module for retrieving this information, but if you can't, SpecuCheck is, at the time of writing, a good alternative.
64 and 32-bit executables can be downloaded from the releases page on the utility's GitHub repo. Open up a command prompt, locate SpecuCheck-x86.exe or SpecuCheck.exe, and run the program. If you have the updates installed, you should see something like this.
The results show each vulnerability and the hardware/software mitigations that are in effect (according to the Windows kernel). Right now, it's just nice information to know, but as we continue to learn more about the extent of the issue, it'll be a handy tool to have available.