I got some info from the FreeBSD website:-
A complete operating system based on 4.4BSD.
FreeBSD's distinguished roots derive from the latest BSD software releases from the Computer Systems Research Group at the University of California, Berkeley. The book The Design and Implementation of 4.4BSD Operating System, written by the 4.4BSD system architects, thus describes much of FreeBSD's core functionality in detail.
Drawing on the skills and experience of a diverse and world-wide group of volunteer developers, the FreeBSD Project has worked to extend the feature set of the 4.4BSD operating system in many ways, striving constantly to make each new release of the OS more stable, faster and containing new functionality driven by user requests.
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FreeBSD provides higher performance, greater compatibility with other operating systems and less system administration.
FreeBSD's developers attacked some of the more difficult problems in operating systems design to give you these advanced features:
A merged virtual memory and filesystem buffer cache continuously tunes the amount of memory used for programs and the disk cache. As a result, programs receive both excellent memory management and high performance disk access, and the system administrator is freed from the task of tuning cache sizes.
Compatibility modules enable programs for other operating systems to run on FreeBSD, including programs for Linux, SCO UNIX, NetBSD, and BSD/OS.
Kernel Queues allow programs to respond more efficiently to a variety of asynchronous events including file and socket IO, improving application and system performance.
Accept Filters allow connection-intensive applications, such as web servers, to cleanly push part of their functionality into the operating system kernel, improving performance.
Soft Updates allows improved filesystem performance without sacrificing safety and reliability. It analyzes meta-data filesystem operations to avoid having to perform all of those operations synchronously. Instead, it maintains internal state about pending meta-data operations and uses this information to cache meta-data, rewrite meta-data operations to combine subsequent operations on the same files, and reorder meta-data operations so that they may be processed more efficiently.
Support for IPsec and IPv6 allows improved security in networks, and support for the next-generation Internet Protocol, IPv6.
Work in-progress includes support for fine-grained SMP locking in kernel, allowing higher performance on multi-processor machines, support for Scheduler Activations, allowing parallelism in threaded programs, filesystem snapshots, fsck-free booting, network optimizations such as zero-copy sockets and event-driven socket IO, ACPI support, and advanced security features such as Mandatory Access Control.
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FreeBSD provides many security features to protect networks and servers.
The FreeBSD developers are as concerned about security as they are about performance and stability. FreeBSD includes kernel support for stateful IP firewalling, as well as other services, such as IP proxy gateways.
FreeBSD also includes support for encryption software, secure shells, Kerberos authentication, "virtual servers" created using jails, chroot-ing services to restrict application access to the file system, secure RPC facilities, and access lists for services that support TCP wrappers.
