wallace@cme-durer.ARPA (Evan Wallace) (10/03/88)
Maybe I missed it, but I never saw any replies to David Blackman's claim that work stations are by defintion real time machines. I will try to keep it brief. In Article <5116@netnews.upenn.edu> David Blackman writes: > ...Jim Morris from Xerox PARC said one of the advantages of the > Alto is that is doesn't run faster at night... This merely implies that Morris thought of the Alto as a single user machine. Furthermore, what PARC originally meant by the term "workstation" does not constrain the present definition. In this context I have always understood the term "workstation" to mean: A primarily single user system often running a UNIX like operating system with a windowing mouse driven user interface and a larger than 80X25 high resolution monitor. Blackman's examples of real-time applications are: > You may be using a remote procedure call. You may have written your > own driver for a serial I/O port. You may have just interfaced a > CD-ROM player to your workstation and are writing a driver for it. > You may be trying to drive a 60 ppm laser printer. You may be > trying to send/receive speech over a network in real time. Or, you > may be experimenting with a new network protocol. All of these can and usually do have processors dedicated to the actual device level control, this is were the real time is done, and not by the workstation. In fact, workstations (as I have defined them) are ill suited for real-time control use. There is a great temptation, however to use them for this. In our Automated Manufacturing Research Facility Suns have been used for the control of manufacturing work-cells. Problems that have come up have been: large but unpredictable messaging delays and queue, FIFO and system resource overruns. These problems resulted in lost data, slow response time or system crash. Moral: don't use ordinary UNIX workstations for real-time control. There are companies like Masscomp that have real-time UNIX systems. Why fight it? Evan Wallace internet wallace@durer.cme.nbs.gov uunet uunet!cme-durer!wallace