Article 170860 of comp.os.vms:
In article <338A488D.6FC7@videotron.ca>,
 jfmezei <"[nospam]jfmezei"@videotron.ca> writes:
> David Cathey (Remove MX to mail) wrote:
>> culmulated into OpenVMS.  The sad thing is Cutler had to capitulate
>> to a Windows assimilation of his theoretically sound base O/S.
>> You'd think he would have taken the tenets of procedure calling
>> standards with him as well.
> 
> I think it is quite pretentious of the VMSer to think that Cutler 
> had so much design authority over NT and that he would have taken
> his VMS knowledge with him.

Not pretentitious at all.  We're simply aware of facts you apparently 
haven't heard about.  

From the internals point of view there is utterly no question that NT 
is VMS re-implemented.  

> Cutler was told to replace DOS with a real kernel over which Windows
> could run, over which teh windows API could run etc etc.

This is off-topic, but you're incorrect here also.  Originally there
wasn't even going to be a Win32 API - 16-bit Windows had not gotten
all that popular when NT was conceived.  NT was originally to be a
follow-on to OS/2, and a cooperative effort with IBM.  But somewhere
along the way Windows got pretty popular, IBM and MS split the beast, 
IBM getting the OS/2 parts and MS keeping the NT parts.

> If you look at the PSION PDA operating system (called EPOC), you'll also
> find many many similarities with VMS. Event Flags, Interprocess
> Mailboxes, shared memory between processes, process priorities, and even
> a utility (SPY) which is the equivalent to SHOW SYS. Its IO system is
> similar to VMS (an equivalent to $ASSIGN with the device name
> determining which driver to use, and $QIO which is more or less
> independant of the device itself.).

That's out at the UI and API level.  We're talking about internal 
similarities.  

> NT is an WINDOWS operating system with modern operating systems
> services. They were implemented with the Windows API mentality.
> Stop thinking that NT is VMS with WINDOWS above it.

No, not "VMS with Windows above it", but a VMS-derived design with 
Windows above it, most certainly. 

> NT differs from DOS in that it has real operating system features, but
> the later are not the exclusivity of VMS.

The "real operating system features" you speak of are at the UI and
API level.  They are not the reasons we consider NT to be a
reimplementation of VMS at the internal level.  

How about:

The scheduler.  (process scheduler in VMS, thread scheduler in NT) 
32 scheduling priorities, divided into the "real-time" (16-31) and 
"variable" (0-15) priority ranges.  identical preemption at ready by 
higher-priority threads; identical quantum and priority boost 
implementations; identical CPU starvation avoidance mechanism to get 
out of priority inversion situations; a null thread for each CPU; 
etc., etc.  

Memory management.  0-7FFFFFFF is per-process, mostly 
user-mode-accessible only; 80000000-FFFFFFFF is systemwide, mostly 
kernel-accessible only.  Functionally identical implementations of 
paging vs. swapping. 

I/O.  I could write a book (in fact, I am), but briefly, IRPs are 
IRPs, UCBs are "device objects", CRBs are "controller objects", ADPs 
are "adapter objects", FDT routines are "dispatch routines", 
EXE$QIODRVPKT is IoStartPacket, StartIO routines are StartIO routines, 
fork routines are DPC routines, ASTs are APCs... etc., etc., etc., 
etc., etc.  

Interrupt handling.  32 levels of interrupts (some simulated but this 
is nevertheless the way the code is written).  IPLs on VMS, IRQLs on 
NT.  In order:  Passive level, APC (AST) Level, Dispatch (fork) level, 
then the IO hardware interrupts, then some "hardware maintenance" 
functions like the hardware timer, IPI, power fail notification, and 
HIGH_LEVEL to block all interrupts. 

Face it, JF, you're wrong.  Worse, you are writing not just in
misunderstanding but in ignorance of the facts.  Please go read
_Showstopper_ and _Inside Windows NT_ (Custer) before opining further
on this subject. 

	--- Jamie Hanrahan, Kernel Mode Systems, San Diego CA
        Internet: jeh@cmkrnl.com (JH645)  CompuServe: 74140,2055  
drivers, internals, networks, applications, and training for VMS and Windows NT
NT driver FAQ, links, and other information:  http://www.cmkrnl.com/

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