Newsgroups: bit.listserv.medlib-l
Date:         Wed, 16 Dec 1992 10:56:00 CST
From:         Sanjay_Chadha@LIBRARY.TMC.EDU
Subject:      DOS in Unix networks

-------------------Laurie Potter's Question---------------------------
I have a question: I understand that you can run DOS
under a Unix network, but I do not understand why it works.
Can anyone explain this??  My specific question is, if your
network operating system is Unix, how can a DOS version of
WordPerfect work, why don't you have to install a UNIX
version of WordPerfect?  I guess I do not understand how
the network operating system runs in the "background" and
is unrelated to the software on it.
----------------------------------------------------------------------
To understand how DOS programs can work under unix networks, you have to
understand how networks work.  Most Local Area Networks work under the
concept of "Fileserver" technology, in contrast to application server or
client server technology.  Client server however, is a broader concept,
and both fileserver and application server share some of it's
characteristics.  Here's what happens in a typical network:

Summary: Essentially a combination of hardware and software makes
available files and programs stored on a remote machine (server) to the
local machine as if it were stored on a local drive connected to the
system.  If this answers your question, you don't have to read any
further!

Objective: Centralize and share data/programs and provide connectivity.

Method: Most LAN serve homogenous machines (Some support heterogenous
machines ie. PCs and Macs, but that gets into other things, classic
example being Internet, which supports all machines) and the LAN
provides a method of connecting machines to themselves (Peer to Peer),
or to a master server (FileServer) or both!  There generally is special
hardware called a Network Interface Card (although not required) and
special software called Network Opearting System (required) that handles
the physical and logical connection to the network.  Each machine's
operating system has to be made aware of the network (DOS 3.0 onwards
only), and has to be provided with a way of addressing the network.
Most networks have a re-director that redirects the operating system
calls to the network where they are answered by the server.  All
comunication on the network follows a set of rules defined by the
"Protocol" being run.  The protocol can be made available for a variety
of platforms eg. TCP/IP for DOS, for MAC, for UNIX and so on.  The
fileserver has to be running the protocol which the workstations are
running or else they cannot talk.  Newer networks allow file servers to
run multiple protocols simultaneously.  Ours runs NBP, XNS and TCP/IP
together, that way, any machine running any of these protocols can
access our fileserver.  That takes care of the connectivity issue.

Now, what a typical LAN server does is file management.  It is like a
central repository (library if you wish) of data and programs that are
to be shared subject to a set of rules (access rights), workstations
send a request to the network for a program, server checks if the
requesting user has access to the program, then if another user is
already using that program, if no other user is using the program,
server will provide the program to the workstation.  The program is then
loaded into the workstations memory and executed there.  THAT IS THE
KEY!  THE program is executed in the workstations memory, NOT THE
SERVERS.  Since the datafiles themselves are stored in a standard format
or a supported format (eg UNIX and SYSTEM 7 support DOS format), they
can be managed by the server without any problems.  eg. Say we have a
unix machine running TCP/IP and we have DOS machine running TCP/IP and
the two are connected to the network.  Now if the UNIX machine is the
server, and stores a copy of Wordperfect for DOS, and the DOS machine
requests it, it will made available to the DOS machine as if the program
was stored on an external drive connected to the DOS machine, which will
load the program as usual in DOS and it will work fine.  However, if we
had a UNIX version of WP on the unix server, and the DOS machine
accessed it, it will get the program all right, but of course, it will
not work as DOS will not answer calls made to the UNIX system.  It will
be just like trying to load WP for UNIX on a DOS standalone machine.

Another example, we have LanManager network which runs under OS/2.  So
our is a OS/2 network.  However, all workstations connected to the
network (except 1) are DOS workstation.  All our programs are DOS
programs that are managed by the OS/2 server, and cannot be run on OS/2
machines that are connected to the network, except in a compatibility
box.  We do have some OS/2 utilities, but NONE of our DOS machines can
run it.

Thus a network file server is an implementation of the "Client Server"
concept at the file level.  The more typical association with the name
is made in regards with databases, where the implementaion is at data
level, and discrete peioces of data are passes to the requesting clients
rather than an entire file.

The third concept I mentioned above is an emerging technology called
application server.  In this technology, the application itself RUNS on
the server, so wordperfect for DOS will actually run on a much faster
server, with it's input and output being controlled by the client
workstation.  Therefore, the operating system running the application
server either must be DOS, or DOS compatible.  With windows requiring
powerful machines, some companies are opting for application servers, so
that each client does not have to be brought up to windows level
machine, instead one powerful server is put in place to run the
application.

Hope this clears it up (as mud?)

Sanjay R. Chadha
HAM-TMC Library, Houston
sanjayc@library.tmc.edu
Comments: Gated by NETNEWS@AUVM.AMERICAN.EDU