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List:       mumps-l
Subject:    Re: DTM and 32-bit Windows
From:       Bob Wells <bobw () INTERSYS ! COM>
Date:       1997-12-24 17:20:05
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At 11:45 AM 11/26/97 -0500, Bruce Hulsey wrote:
[snip]

>If I want to develop a VB+M application I really don't see any advantages of
>Cache over DTM.  Sure, Cache offers a relational layer (if you pay extra
for it)
>and I hear that the newer version offers an object layer but plain M suits me
>just fine for my database servers.  If one does not use the relational or
object
>features then Cache puts small single user application developers at a
>disadvantage (one has to start and stop the server manually unless you
want the
>server running all the time, 50mb footprint, etc).  The _only_ advantage
that I
>see is that one can develop 32 bit clients that will talk to the M server
on the
>same machine.  With DTM one is fairly well limited to using 16 bit VB 3 to
>exploit the full capabilities of Visual M.  Again, I say, why not give 32 bit
>access to DTM via pipes, ip loopback address, etc.?

Since this complaint keeps coming up, I thought I'd repeat the explanation
that's been made before re DTM and local access.

DTM is a (very) DOS program. (It is not a Windows program. It does not have
access to any Windows features.) Much of it is assembly langauge, and it
has intimate knowledge of the DOS environs, including explicit page
swapping, etc. As such, it does not have access to any 32-bit world. (As a
particular example, VxDs are a mechanism to communicate between 16-bit
virtual machines, e.g., Win 3.1 and DOS. This was not adequately emulated
in Windows NT 3.51, for example, leading to the inability to run DTM under
NT until 4.0 was released.) Also - and for the same reasons - to use TCP,
it must use 16-bit TCP. But if you have Win95 or NT on your machine and you
want to talk to a Windows client, you have to have Windows TCP installed.
But you can't have two TCPs installed and running on the same machine at
the same time.

So - the operating system does not provide VxD access from 32 bits, and TCP
cannot be used locally in this environment. So the only available
arrangement for a thick DTM client is DTM (under DOS) talking through VxD
to Windows (3.1/95). Pipes are not available to DOS; TCP loopback is not
available to DOS. The man-years of effort required to do a major rework of
DTM to work around these problems simply don't make sense. Instead, Cache
was built as the next generation, portable across 32-bit operating systems
and including many of the best features of multiple M versions - including
DTM - and lots more.

On the other hand, DTM still works just fine as a server to thin clients of
all kinds using TCP, since that does not incur any of the restrictions
described above.

Hope this clears up some confusion.

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