2.  System Development

      The first phase of each Berkeley system is its development. CSRG maintains a continuously evolving list of projects that are candidates for integration into the system. Some of these are prompted by emerging ideas from the research world, such as the availability of a new technology, while other additions are suggested by the commercial world, such as the introduction of new standards like POSIX, and still other projects are emergency responses to situations like the Internet Worm.

      These projects are ordered based on the perceived benefit of the project as opposed to its difficulty; the most important are selected for inclusion in each new release. Often there is a prototype available from a group outside CSRG. Because of the limited staff at CSRG, this prototype is obtained to use as a starting base for integration into the BSD system. Only if no prototype is available is the project begun in-house. In either case, the design of the facility is forced to conform to the CSRG style.

      Unlike other development groups, the staff of CSRG specializes by projects rather than by particular parts of the system; a staff person will be responsible for all aspects of a project. This responsibility starts at the associated kernel device drivers; it proceeds up through the rest of the kernel, through the C library and system utility programs, ending at the user application layer. This staff person is also responsible for related documentation, including manual pages. Many projects proceed in parallel, interacting with other projects as their paths cross.

      All source code, documentation, and auxiliary files are kept under a source code control system. During development, this control system is critical for notifying people when they are colliding with other ongoing projects. Even more important, however, is the audit trail maintained by the control system that is critical to the release engineering phase of the project described in the next section.

      Much of the development of BSD is done by personnel that are located at other institutions. Many of these people not only have interim copies of the release running on their own machines, but also have user accounts on the main development machine at Berkeley. Such users are commonly found logged in at Berkeley over the Internet, or sometimes via telephone dialup, from places as far away as Massachusetts or Maryland, as well as from closer places, such as Stanford. For the 4.3BSD release, certain users had permission to modify the master copy of the system source directly. People given access to the master sources are carefully screened beforehand, but are not closely supervised. Their work is checked at the end of the beta-test period by CSRG personnel who back out inappropriate changes. Several facilities, including the Fortran and C compilers, as well as important system programs, for example, telnet and ftp, include significant contributions from people who did not work directly for CSRG. One important exception to this approach is that changes to the kernel are made only by CSRG personnel, although the changes are often suggested by the larger community.

      The development phase continues until CSRG decides that it is appropriate to make a release. The decision to halt development and transition to release mode is driven by several factors. The most important is that enough projects have been completed to make the system significantly superior to the previously released version of the system. For example, 4.3BSD was released primarily because of the need for the improved networking capabilities and the markedly improved system performance. Of secondary importance is the issue of timing. If the releases are too infrequent, then CSRG will be inundated with requests for interim releases. Conversely, if systems are released too frequently, the integration cost for many vendors will be too high, causing them to ignore the releases. Finally, the process of release engineering is long and tedious. Frequent releases slow the rate of development and cause undue tedium to the staff.