functions interact with a database system running in user mode. Functions are also sometimes moved across rings in the other direction. The Linux kernel, for instance, injects into processes a vDSO section which contains functions that would normally require a system call, i.e. a ring transition. Instead of doing a syscall these functions use static data provided by the kernel. This avoids the need for a ring transition and so is more lightweight than a syscall. The function gettimeofday can be provided this way. Hypervisor mode Recent CPUs from Intel and AMD offer x86 virtualization instructions for a hypervisor to control Ring 0 hardware access. Although they are mutually incompatible, both Intel VT-x (codenamed "Vanderpool") and AMD-V (codenamed "Pacifica") create a new "Ring −1" so that a guest operating system can run Ring 0 operations natively without affecting other guests or the host OS. To assist virtualization, VT-x and SVM insert a new privilege level beneath Ring 0. Both add nine new machine code instructions that only work at "Ring −1", intended to be used by the hypervisor. Privilege level A privilege level in the x86 instruction set controls the access of the program currently running on the processor to resources such as memory regions, I/O ports, and special instructions. There are 4 privilege levels ranging from 0 which is the most privileged, to 3 which is least privileged. Most modern operating systems use level 0 for the kernel/executive, and use level 3 for application programs. Any resource available to level n is also available to levels 0 to n, so the privilege levels are rings. When a lesser privileged process tries to access a higher privileged process, a general protection fault exception is reported to the OS. It is not necessary to use all four privilege levels. Current operating systems with wide market share including Microsoft Windows, macOS, Linux, iOS and Android mostly use a paging mechanism with only one bit to specify the privilege level as either Supervisor or User (U/S Bit). Windows NT uses the two-level system. The real mode programs in 8086 are executed at level 0 (highest privilege level) whereas virtual mode in 8086 executes all programs at level 3. Potential future uses for the multiple privilege levels supported by the x86 ISA family include containerization and virtual machines. A host operating system kernel could use instructions with full privilege access (kernel mode), whereas applications