Re: Whither goest DOS?

> Frankly, I will be dancing in the clouds when MS finally stops

supporting that

> library-cum-virus-cum-"operating environment" that passes for

an "operating

> system", i.e. Windows 2, 3, 3.1, WFW 3.11, Win95, Win95 OSR2,

Win98, and Win ME.

> It is unfortunate that some form of DOS does not remain available

as a remnant.

> I think most of us here would be happy if we could buy a DOS

license on a

> completely-unsupported basis...

Kevin,

I understand your frustration with windows, but I think your goals
are somewhat in conflict. On the one hand you want a well written
operating system that enforces rules to keep poorly written
applications from stepping on eachother's turf. On the other,
you want 'real' dos with 'real' basically meaning freedom
to step on priveleged system turf such as IO ports or the system
timer.

The conflict can of course be worked out in at least two ways:

1) Run 'real' dos on dedicated machines that do nothing but cnc
control. I'm not sure if you were complaining that you could no
longer buy it for this purpose.

or

2) Implement ways to grant privileges only to selected applications so
that they can do things like mess with the timer or directly write
to IO ports.

The linux/EMC system uses option (2) - the realtime scheduler runs
above the operating system with no rules. Tasks running under the
linux kernel with root permissions can setup realtime tasks above the
kernel, which are easily capable of crashing the system. To gain
IO port access from a normal linux task you need to have root
permission and specifically request access to that port. Presumably
such a request could be refused or at least logged if one were
attempting to debug an unstable system. Meanwhile ordinary tasks
running with user permissions are limited in the amount of damage
they can do, much as theoretically takes place under NT.

It may be that NT and its dervitatives, when working properly,
provide the necessary hooks to get at the hardware features needed to
write a high performance, reliable motion system if one takes the
time (and perhaps signs enough NDA's) to learn how. I know one
ancestor of EMC used such a base system. But the open source nature
of linux has substantial advantages whenver one desires to do things
not anticipated by the operating system vendor.

Chris Stratton