Editing RTLinux (section)

== Implementation ==
RTLinux provides the ability to run special real-time tasks and interrupt handlers on the same machine as standard Linux. These tasks and handlers execute when they need to execute no matter what Linux is doing. The worst case time between the moment a hardware interrupt is detected by the processor and the moment an interrupt handler starts to execute is under 15 microseconds on RTLinux running on a generic x86 (circa 2000). A RTLinux periodic task runs within 35 microseconds of its scheduled time on the same hardware. These times are hardware limited, and as hardware improves RTLinux will also improve. Standard Linux has excellent average performance and can even provide millisecond level scheduling precision for tasks using the POSIX soft real-time capabilities. Standard Linux is not, however, designed to provide sub-millisecond precision and reliable timing guarantees. RTLinux was based on a lightweight virtual machine where the Linux "guest" was given a virtualized interrupt controller and timer, and all other hardware access was direct. From the point of view of the real-time "host", the Linux kernel is a thread. Interrupts needed for deterministic processing are processed by the real-time core, while other interrupts are forwarded to Linux, which runs at a lower priority than real-time threads. Linux drivers handled almost all [[I/O]]. First-In-First-Out pipes ([[FIFO (computing and electronics)|FIFO]]) or shared memory can be used to share data between the operating system and RTLinux.