Allegro CL 9.0 with SMP is now released and available on Windows, the Mac, and Linux. We will be having a series of Tech Corner articles on using SMP. In this one, we discuss some atomic operations. These are special versions of standard Lisp store or read/modify/store operations which are guaranteed to work in SMP. We will show examples where using the standard operations will fail but the atomic operations will succeed, and give some cautions about what success means. Click here to see the article.