[Info-vax] Hard links on VMS ODS5 disks

[John Dallman]

In article <u9dslr$385j1$1 at dont-email.me>,
clubley at remove_me.eisner.decus.org-Earth.UFP (Simon Clubley) wrote:
> On 2023-07-20, Dave Froble <davef at tsoft-inc.com> wrote:
> > I can also imagine a "brand-new architecture" where a port of 
> > Linux just might not be so easy.
> People didn't have much of a problem getting it onto RISC-V, which 
> is indeed a brand-new architecture that also needed major compiler 
> work.

There are network externalities here. The things that Linux assumes about
a machine are fairly simple. They probably amount to something like: 

* Byte addressing. Endianness is not important. 
* Flat address space big enough for any single program. 
* Some kind of memory protection system. Paging is optional. 
* Some kind of interrupt priority system. 
* User and supervisor modes. 

Designing a new architecture that cannot meet these requirements means
you /must/ design a new operating system for it, and you cannot readily
take advantage of the large amounts of useful open-source software that
are out there. So nobody will do that, unless they have a really
compelling idea about computing that can't be made compatible with Linux
requirements. There don't seem to be many of those coming along at
present. 

Note that these requirements are a subset of VMS' requirements, and all
of VMS' hardware platforms are fully capable of running Linux. The only
one where that hasn't been done on any scale is VAX, simply because VAX
was already on the way out when Linux started to grow out of its original
x86 niche. 

I also read comp.arch, where there is a community of people who design
new processor architectures, either professionally or for fun. There are
at least two people there who as hobby projects have designed a new
architecture, implemented it in an FPGA, and got Linux running on it,
either by themselves or with one or two people's help. I don't know how
long it's taken them, but I think it's less than nine years. 

The strangest new architecture that gets discussed there regularly is The
Mill <https://millcomputing.com/>. This has no registers in the
conventional sense, and two program counters per thread, but the
operating system they're porting to it is Linux. 

John