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Undid revision 1282192002 by Liz (talk) article restored

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{{short description|Novell-compatible computer-readable software}}
{{Use mdy dates|date=July 2021}}
{{use American English|date=July 2021}}
{{Infobox file format
| name = NetWare Loadable Module
| icon =
| extension = .nlm
| mime =
| owner = [[Novell]]
| typecode =
| magic = NetWare Loadable Module
| genre = [[Executable]], [[Shared library]]
| containerfor =
| containedby =
| extendedfrom =
| extendedto =
| standard =
}}
A '''NetWare Loadable Module'''<ref>{{cite news |newspaper=[[Computerworld]]
|url=https://www.computerworld.com/article/2307524/revelation--a-netware-loadable-module-that-s-still-around.html
|title=Revelation: A NetWare Loadable Module that's still around
|author=Dave Kearns |date=October 3, 2006}}</ref><ref>{{cite news |newspaper=[[Computerworld]]
|url=https://www.computerworld.com/article/2299449/database-server-choices-for-netware.html
|title=Database server choices for NetWare}}</ref><ref>{{cite news |newspaper=[[Computerworld]]
|url=https://www.computerworld.com/article/2569895/hands-on--getting-macs-and-pcs-to-play-well-together.html
|title=Hands on: Getting Macs and PCs to play well together}}</ref> ('''NLM''') is a [[loadable kernel module]] (a [[Binary file|binary]] code module) that can be loaded into [[Novell NetWare|Novell's NetWare]] operating system. NLMs can implement hardware drivers, server functions (e.g. clustering), applications (e.g. [[GroupWise]]), system libraries or utilities.

NLMs were supported beginning with the [[i386|Intel 80386]]-based [[NetWare#NetWare 3.x|NetWare]] version 3.x. Prior versions of NetWare had a monolithic [[Kernel (operating system)|kernel]], and significant hardware or functionality changes required re-linking the kernel from object modules.

Due to stability issues with early third-party NLMs, they never became popular for server application programming, with few exceptions like [[antivirus software|antivirus]] programs, [[backup]] programs and certain [[database]] products.

==Functionality==
Upon loading, a NLM requests resources, such as memory and process threads, from the NetWare kernel. The NetWare kernel tracks such requests, and can identify memory and other resources assigned to a specific NLM. NLMs may auto-load other NLMs upon which they themselves depend.

NLMs may register commands with the NetWare kernel, extending the command vocabulary available at the NetWare console prompt.

When properly coded, NLMs can be re-entrant, allowing multiple instances of the same code to be loaded and run.

==Programming issues==
Initially, Novell published a development toolkit for NLM programming including kernel API documentation and a [[C (programming language)|C compiler]] ([[Watcom]]), but third-party support for the NLM executable function was very limited.

In early NetWare versions (prior to v4.x), all processes were executed in the [[Kernel (operating system)|kernel]] address space, without specific memory protection. It was therefore possible for [[Software bug|bug]]s in NLMs to overwrite the kernel's or other NLM's address space and ultimately crash the server — in the mainframe-derived Novell terminology, this was known as an ABEND or [[Abnormal end|ABnormal END]].

Moreover, NetWare used a non-preemptive, or [[co-operative multitasking|cooperative]], multitasking model, meaning that an NLM was required to yield to the kernel regularly.<ref>{{cite book
|title=NetWare Administration: NetWare 4.0-6.0
|author=Mark Foust |year=2001}}</ref> An NLM executing an [[infinite loop]], for example, could therefore not be stopped.

In NetWare v4.x, Novell introduced a limited form of memory protection, which was extended to ''Protected Address Spaces'' in NetWare v5.x. Through these mechanisms, properly-coded NLMs can be loaded into their own address space, and mis-behaving NLMs can be prevented from compromising the kernel integrity.

==Compilers==
Official compilers that produce NLMs are:

* [[Watcom C/C++|Watcom C/C++ compiler]] / [[Watcom C/C++|OpenWatcom]]
* [[Metrowerks]] [[CodeWarrior]] for NetWare<ref name="Metrowerks"/>
* EPC C/C++
* Novell NLMLINK.EXE

NLM development is also possible with GNU cc and binutils.<ref name="NLM_Linux"/> More details are available in NetWare Loadable Module Programming HOWTO by Martin Hinner.<ref name="NLM_Howto"/>

==Client-side NLMs with NIOS==
Announcing it in March 1995,<ref name="Network_World_1995"/><ref name="PCMag_1995"/> Novell introduced a new 32-bit DOS/Windows [[Personal NetWare#NetWare clients for DOS|NetWare]] client ([[Client 32]] based on ODI32/NIOS)<ref>{{cite web
|url=https://encyclopedia2.thefreedictionary.com/Netware+Input%2FOutput+Subsystem
|title=Netware Input/Output Subsystem}}</ref> in 1996, replacing the former 16-bit client based on [[Open Data-Link Interface|ODI]]/VLM. Its NIOS component ([[NetWare I/O Subsystem]]<ref name="Network_World_1995"/><ref name="Liebing_1996"/><ref name="Hendrick_1996"/>) used techniques similar to [[DOS Protected Mode Services|DPMS]] to relocate and run NLMs in [[protected mode]] and [[extended memory]] in order to reduce the [[conventional memory]] footprint of the client down to 2 to 5 KB.<ref name="Paul_1997_NWDOSTIP"/><ref name="Liebing_1996"/>

==See also==
* [[Virtual Loadable Module]] (VLM)

==References==
{{Reflist|refs=
<ref name="Metrowerks">{{cite web |title=Metrowerks website |url=http://www.metrowerks.com/ |url-status=dead |archive-url=https://web.archive.org/web/20090106143416/http://metrowerks.com/ |archive-date=2009-01-06}}</ref>
<ref name="NLM_Linux">{{cite web |url=http://martin.hinner.info/nlm/ |title=NLM development under Linux}}</ref>
<ref name="NLM_Howto">{{cite web |title=NetWare Loadable Module Programming HOWTO |url=http://martin.hinner.info/nlm/NLM-HOWTO/NLM-HOWTO.html}}</ref>
<ref name="Network_World_1995">{{cite journal |title=Novell to dress up Tuxedo and deliver 32-bit client |date=1995-03-27 |journal=[[Network World]] |page=141 |url=https://books.google.com/books?id=ShgEAAAAMBAJ&pg=PA141 |access-date=2018-08-18}}</ref>
<ref name="PCMag_1995">{{cite journal |title=Network Edition - Cover Story |date=1995-10-24 |journal=[[PC Magazine]] |page=NE27 |url=https://books.google.com/books?id=3jNOHGmrpRkC&pg=PA527 |access-date=2018-08-18}}</ref>
<ref name="Liebing_1996">{{cite web |title=NetWare Client 32 for DOS/Windows: Overview of Architecture and Features |author-first=Edward A. |author-last=Liebing |date=1996-05-01 |publisher=[[Novell]] |work=Novell AppNotes |url=https://support.novell.com/techcenter/articles/ana19960501.html |access-date=2018-08-18 |url-status=live |archive-url=https://web.archive.org/web/20180818204926/https://support.novell.com/techcenter/articles/ana19960501.html |archive-date=2018-08-18}}</ref>
<ref name="Hendrick_1996">{{cite web |title=Overview of NetWare Client 32 for Windows 95 |author-first=Ben |author-last=Hendrick |date=1996-11-01 |publisher=[[Novell]] |work=Novell AppNotes |url=https://support.novell.com/techcenter/articles/ana19961101.html |access-date=2018-08-18 |url-status=live |archive-url=https://web.archive.org/web/20180818205427/https://support.novell.com/techcenter/articles/ana19961101.html |archive-date=2018-08-18}}</ref>
<ref name="Paul_1997_NWDOSTIP">{{cite book |title=NWDOS-TIPs — Tips & Tricks rund um Novell DOS 7, mit Blick auf undokumentierte Details, Bugs und Workarounds |work=MPDOSTIP |author-first=Matthias R. |author-last=Paul |date=1997-07-30 |edition=3 |version=Release 157 |language=de |url=http://www.antonis.de/dos/dos-tuts/mpdostip/html/nwdostip.htm |access-date=2012-01-11 |url-status=live |archive-url=https://web.archive.org/web/20160522014302/http://www.antonis.de/dos/dos-tuts/mpdostip/html/nwdostip.htm |archive-date=2016-05-22}} (NB. NWDOSTIP.TXT is a comprehensive work on [[Novell DOS 7]] and [[OpenDOS 7.01]], including the description of many undocumented features and internals. It is part of the author's yet larger MPDOSTIP.ZIP collection maintained up to 2001 and distributed on many sites at the time. The provided link points to a HTML-converted older version of the NWDOSTIP.TXT file.)</ref>
}}

==Further reading==
* {{cite book |title=NetWare 386 Programmer's Guide |author-first=Ralph |author-last=Davis |publisher=[[Addison-Wesley]] |date=1991 |isbn=978-0-201-57709-9}}
* {{cite web |title=Novell Developer Documentation: Netware Loadable Module |url=http://developer.novell.com/tech/nlm.html |access-date=2010-09-25 |url-status=dead |archive-url=https://web.archive.org/web/20091124201302/http://developer.novell.com/tech/nlm.html |archive-date=2009-11-24}}

[[Category:Executable file formats]]
[[Category:Novell NetWare]]

NetWare Loadable Module - Revision history

imported>Kvng: Undid revision 1282192002 by Liz (talk) article restored