In the Linux operating system, the Native POSIX Thread Library (NPTL) is a software feature that enables the Linux kernel to run programs written to use POSIX-style threads very efficiently.
In tests, it succeeded in running 100,000 threads simultaneously on a IA-32 which were started in two seconds. In comparison, this test under a kernel without NPTL would have taken around 15 minutes.
History
NPTL first came out in Red Hat 9.0. Old-style POSIX threading is known for having trouble with threads that refuse to yield to the system occasionally because it does not take the opportunity to preemptively yield them when it arises, something that Windows was known to do better at the time. Red Hat claimed that NPTL fixed this problem in an article on the Java website about Java on Red Hat 9.
NPTL vs. Windows Threading Experiments
In research done by Edward Rice in February of 2004, NPTL was compared to the Windows Threading Library. A program written in Java created multiple threads that ran at the same time. This program was run on both Windows and Linux on a dual boot system Intel non-hyper-threading chipset. It was discovered that Windows handled threads that yielded often better than Red Hat Linux 9, but Red Hat Linux 9 handled threads that yielded less frequently better than Windows. It was concluded that this was the result of the time it takes for a thread to yield and the virtual machine to pick a new one.