Re: How do I know if I want Linux

Don Hughes wrote:

> My question is, how do I, myself, know and justify the reason that I
> would want to have Linux on my system with a partition for Linux
> exclusively to do other tasks?
>
> I have heard and seen here many messages from the Linux/EMC guru's here,
> and with the amount of controller software for Windows systems, I am
> having a hard time to seek a reason why I would need two O/S's.
>
> Can someone please try to explain to me and any others that might be in
> the same predicament as myself about these decisions.

NIST started out trying to make the EMC project run under Windows
NT. It ran, but required a $2000 per machine real time extension.
NIST couldn't develop this itself, because the internals of NT are
not made public, you have to buy a $10,000 subscription to get
that sort of info. (Individuals can get it cheaper, but NIST looks
like deep pockets to M$.)

They bought the RT extension, and did a number of timing tests.
If you ran the servo loops on a dedicated processor (like the
$4000 Delta Tau motion card) then the trajectory planning
ran quite well on the PC. But, the interrupt latency was way
too high for the servo loops to be run on the PC's own
processor. I think there were reliability problems with NT,
too.

After getting a machine working, the team at NIST started looking
at alternatives, and tested the early real time patches for Linux,
and found the interrupt latency to be astoundingly low! This meant
that the servo loops could be run on the PC's processor, and the
expensive Delta Tau card wasn't needed. The Servo-to-Go
card is just encoder counters and DAC's (plus some digital I/O)
and is only $888 for 8 axes. Dropping the $2000 RT extensions
to NT, and the cheaper servo card, plus the knowledge that
any detail of the Linux internals could be doped out by just reading
the code, made this look so much more approachable to the
NIST team. A retrofitter and end-user who is lucky to live
near the NIST site has been filling me in on details of how this
all came about as we worked through various stages of the
development. The first Linux version came out about Nov 1997,
I think. It took me until about Aug 98 to get it running well
enough to cut metal with it.

Yup, I'd rather just have one system to support, and thought
seriously about going to NT at one time. But, there is nothing
else like EMC available as totally open source, that I'm aware
of. And, I really needed open source, so I could understand
it. (Great manuals could get around that, but who has great
manuals?)

I have a computer totally dedicated to the machine shop, and
I only start MS DOS on it once a year or so, when something
goes totally haywire, and I want to run the Servo-to-Go
diagnostic program, or some similar situation.

Jon