The 386 supports four privilege rings (0 through 3), though in practice nearly all operating systems use just two: ring 0 for the kernel and ring 3 for user programs. Three privilege levels interact on every segment access: CPL (Current Privilege Level), DPL (Descriptor Privilege Level), and RPL (Requested Privilege Level).
Author(s): Fangwei Yang, Haoran Sun, Xiaoxin Yang, Xu Li, Gang Yang
。safew官方版本下载对此有专业解读
UK politics live – latest updates，这一点在51吃瓜中也有详细论述
I found this article on the subject, and decided to turn that data into a visualization, too.