[3] FreeBSD 3.0 was the first branch able to support symmetric multiprocessing (SMP) systems, using a Giant lock and marked the transition from a.out to ELF executables.
[5] FreeBSD 4 was lauded for its stability, was a favorite operating system for ISPs and web hosting providers during the first dot-com bubble,[dubious – discuss] and is widely regarded[by whom?]
Among the new features of FreeBSD 4, kqueue(2) was introduced (which is now part of other major BSD systems) and Jails, a way of running processes in separate environments.
[7] After almost three years of development, the first 5.0-RELEASE in January 2003 was widely anticipated, featuring support for advanced multiprocessor and application threading, and for the UltraSPARC and IA-64 platforms.
The largest architectural development in FreeBSD 5 was a major change in the low-level kernel locking mechanisms to enable better symmetric multi-processor (SMP) support.
Other major changes included an M:N native threading implementation called Kernel Scheduled Entities (KSE).
FreeBSD 5 also significantly changed the block I/O layer by implementing the GEOM modular disk I/O request transformation framework contributed by Poul-Henning Kamp.
GEOM enables the simple creation of many kinds of functionality, such as mirroring (gmirror), encryption (GBDE and GELI).
These versions extended work on SMP and threading optimization along with more work on advanced 802.11 functionality, TrustedBSD security event auditing, significant network stack performance enhancements, a fully preemptive kernel and support for hardware performance counters (HWPMC).
New features included SCTP, UFS journaling, an experimental port of Sun's ZFS file system, GCC4, improved support for the ARM architecture, jemalloc (a memory allocator optimized for parallel computation,[8] which was ported to Firefox 3),[9] and major updates and optimizations relating to network, audio, and SMP performance.
Inclusion of improved device mmap() extensions enables implementation of a 64-bit Nvidia display driver for the x86-64 platform.
A pluggable congestion control framework, and support for the ability to use DTrace for applications running under Linux emulation were added in FreeBSD 8.3.
The PlayStation 4 video game console uses a derived version of FreeBSD 9.0, which Sony Computer Entertainment dubbed "Orbis OS".