[Info-vax] Hard links on VMS ODS5 disks

[Dan Cross]

In article <memo.20230721201301.21172K at jgd.cix.co.uk>,
John Dallman <jgd at cix.co.uk> wrote:
>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.

It strikes me that these two things (an OS for an "unusual"
architecture lacking one or more of the requirements listed
above, and the ability to make use of the large body of
open-source software) are mostly orthogonal.  Indeed, many
useful OSS packages are available for a variety of wildly
different systems.

Sure, things that are Linux-specific (or Unix/POSIX-specific
more generally) won't be readily portable to other systems, but
the universe of useful open source userspace software is very
large, and much of it could run on, say, a machine that doesn't
support interrupts or user/supervisor modes.

>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. 

I'm not sure about that; we see lots of accelerator processors
that don't implement a traditional ISA and they run lots of
stuff.

>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. 

I'll believe in the Mill when I see it. :-D

	- Dan C.