UNIX Filesystems: Evolution, Design, and Implementation

System V Release 4 and Variants

System V Release 4 set the standard for everyone else to follow producing an extremely feature-rich operating system that combined the best of the historical versions of UNIX with many new ideas from Sun. The following list shows some of the major enhancements that came with SVR4:

• The VFS/vnode architecture that replaced the FSS from SVR3. The VFS/vnode architecture was originally developed as part of SunOS.
• Symbolic links.
• The C and Korn Shells along with job control.
• Memory mapped files.
• The UFS filesystem derived from the BSD Fast File System. UFS became the defacto standard on most versions of UNIX. It is still the default filesystem on Solaris and is still undergoing major development. SVR4 also included the NFS filesystem. At this stage, the largely unsuccessful RFS was starting to fade.
• STREAMS-based console and TTY (teletype) management.
• Real-time scheduling and a partial implementation of kernel preemption.

Enhancements continued thereafter. SVR4.1 included Asynchronous I/O. SVR4.2 included Access Control Lists (ACLs), the VERITAS Filesystem (VxFS), and VERITAS Volume Manager (VxVM). Following this, with a major rewrite, SVR4.2MP introduced Symmetric Multiprocessing (SMP) capabilities and kernel threads.