John Alvord wrote:
>
> On Wed, 23 Aug 2000 12:35:53 +0200, Daniel Phillips wrote:
>
> >To illustrate, I'll go back - way back - to the only device I've ever
> >used where this worked properly: an IBM 3270 series terminal. On a
> >3270, if you type when the system isn't ready for you, your input still
> >appears on the screen - in a line overlaid on top of the regular
> >display. When you hit enter the line disappears and you can enter
> >another one. When the system (a mainframe) finally gets around to you
> >it queries the terminal controller for input, which alerts the 3270 to
> >the fact that the typeahead window should now go away and be replaced by
> >the underlying text. Presumeably your input is then echoed in a form
> >chosen by the application.
>
> The 3270 hardware itself locks up when an AID (such as enter) key is
> pressed. Some program has to send a control sequence to unlock the
> keyboard. During the interval, an attempted to type will result in a
> temporary lockup with a big X on the status line.
>
> What you saw was probably the VM operating system. I was a VM hacker
> in the good old days and the above was made possible by some kernel
> (CP) level code which captured the input, queued it, and unlocked the
> 3270. The user space application was unaware of the situation.
It was MTS - Michigan Terminal System - which was kind of an early Open
Source effort shared amongst universities, much like Linux except for
mainframes and with Fortran instead of C. MTS had many advanced and
comfortable features, particularly in the area of interactive
development and graphics, some of which I haven't seen equaled even
today. I had no idea that the rest of the mainframe world was made to
suffer in the way you described. On MTS the only time you would ever
see the dreaded X was when there were more than about 200 users on the
system. Which consisted, by the way, of one Amdahl 470 with 4 meg
memory, a little more powerful than a 486.
[...]
> So the behavior you observed was from a kernel hack much like the
> current Linux scheme.
I'm not completely sure about this, but I think it was actually a
channel program hack, and I can assure you that it worked much better
than the current Linux scheme.
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