[Info-vax] Prism/Pillar, was: Re: inertia or fundamentals about langages?

[Stephen Hoffman]

On 2019-05-29 12:21:11 +0000, Simon Clubley said:

> On 2019-05-28, Stephen Hoffman <seaohveh at hoffmanlabs.invalid> wrote:
> 
>> The production ports of OpenVMS for Alpha and Itanium were interesting  
>> and technically complex and challenging in various ways, but haven't 
>> particularly diverged from the design and organization of the 
>> progenitor VAX modular kernel.
> 
> Should that be monolithic, instead of modular ?
> 
> I wouldn't exactly call the VMS kernel modular, especially by today's 
> standards.

Donno.  I've always called it "modular", though "modular monolithic" 
might be closer to current terminology.

While the OpenVMS kernel uses a monolithic address space, the 
organization of the kernel itself is not monolithic and the various 
pieces of the kernel are dynamically linked together during and 
variously after bootstrap.

Prior to V5.0, VAX/VMS was rather closer to monolithic in its kernel design.

The development work on the VAX/VMS V5 kernel changes—what many DEC VMS 
folks have long referred to as the "exec" or "executive"—was known as 
the "modular executive".
https://archive.org/details/bitsavers_decvaxvms5leaseNotesApr88_16389799

As for the terminology, "Modular operating systems such as OS-9 and 
most modern monolithic operating systems such as OpenVMS, Linux, BSD, 
SunOS, AIX, and MULTICS can dynamically load (and unload) executable 
modules at runtime."  Contrary to that parenthetical and here ignoring 
user-written system service code (also known as privileged sharable 
images), OpenVMS can load but typically cannot unload kernel code. 
Reloading can be dicy.
https://en.wikipedia.org/wiki/Monolithic_kernel

Terminology shifts, too.  I once tried finding "firewall" in the 
Process MultiNet documentation, for instance.  Same for HBVS RAID-1.

If this discussion follows one of the usual courses, there would 
usually soon be some confusion posted around macOS and the XNU kernel. 
"XNU is a hybrid kernel, containing features of both monolithic kernels 
and microkernels, attempting to make the best use of both technologies, 
such as the message passing ability of microkernels enabling greater 
modularity and larger portions of the OS to benefit from memory 
protection, and retaining the speed of monolithic kernels for some 
critical tasks."
https://en.wikipedia.org/wiki/XNU

Kernel and operating system designs are an endless series of design trade-offs.



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