Windows had this length limit all the up to and including Win8, my work login which included a 3 letter domain and backslash was too long for Windows, so they cut the last 3 letters of my name off so that I could be logged in. It's made logging in to to some work services difficult, I'm not always sure they are asking for full ID like email address, or the truncated version.
10 isn't much better if you're using a Microsoft account. My email follows the format "fmlastname@gmail.com" (and is coincidentally the exact same character count). My user directory gets shortened to "fmlas".
