HARDWARE AND SOFTWARE ENVIRONMENT

On Linux OS

The PDP-11/70 on which the Research Unix system is installed is a 16-bit word (8-bit byte) computer with 768K bytes of core memory; the system kernel occupies 90K bytes about equally divided between code and data tables. This system, however, includes a very large number of device drivers and enjoys a generous allotment of space for I/O buffers and system tables, a minimal system capable of running the software mentioned above can require as little as 96K bytes of core altogether. There are even larger installations, see the description of the PWB/UNIX systems (4, 5), for example. There are also much smaller, though somewhat restricted, versions of the system [6].

Our own PDP-11 has two 200-Mb moving-head disks for file system storage and swapping. There are 20 variable-speed communications interfaces attached to 300- and 1200-baud data sets, and an additional 12 communication lines hard-wired to 9600-baud terminals and satellite computers. There are also several 2400- and 4800-baud synchronous communication interfaces used for machine-to-machine file transfer. Finally, there is a variety of miscellaneous devices including nine-track magnetic tape, a line printer, a voice synthesizer, a phototypesetter, a digital switching network, and a chess machine.

The preponderance of Unix software is written in the abovementioned C language [7]. Early versions of the operating system were written in assembly language, but during the summer of 1973, it was rewritten in C. The size of the new system was about one-third greater than that of the old. Since the new system not only became much easier to understand and to modify but also included many functional improvements, including multiprogramming and the ability to share reentrant code among several user programs, we consider this increase in size quite acceptable.

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