[Info-vax] Hard links on VMS ODS5 disks

[Arne Vajhøj]

On 7/20/2023 8:49 AM, Simon Clubley wrote:
> I keep looking at why the port is currently at 9 years and counting
> compared to how long it takes to port Linux to a brand-new architecture
> and keep wondering why it is taking so long.
> 
> There are some things you have had to implement, such as KESU emulation,
> that Linux doesn't have to deal with, but I have a hard time seeing why
> that would take more than a few months to design and implement.

The 9 years do raise some questions, but some answers are known.

Why has Itanium->x86-64 taken longer time than VAX->Alpha and
Alpha->Itanium?

It has been explained that is because VSI got fewer engineers than
DEC and HP.

Why does it take so long when any CS student can do a port of some
nix flavor in a semester?

VMS has 2 constraints:
- it has to be commercial grade (rock solid, complete etc.)
- it has to be 100% compatible

Everybody that has done software development knows that it
takes 10-100 times more time to do a commercial grade
production ready product than an experimental test product.

And 100% compatibility instead of just 98% compatibility
is also a burden that prevents the easy shortcuts.

Why does VMS port take longer than a Linux port?

First we need to make sure that the Linux port is
comparable per above. Some of the few that comes to my
mind is IBM's ports to Power and mainframe. I have
no idea how long time IBM spent on that.

But let us assume IBM did spend less time than VSI
on VMS x86-64.

VMS is probably less portable than Linux in design.

VMS was designed in parallel with VAX - the OS people
could ask the HW people for what they needed.

The 64 bit port to Alpha was also to something
controlled by DEC and they could create PALcode
for what they needed.

Linux was designed in a world where the HW specs
were externally given.

Now VMS is in that world as well - VSI cannot call
Intel/AMD and ask to get a few instructions added.

It is not just the only 2 modes.

The VSI people have also mentioned the lack of probe
as an issue.

There are probably a number of issues in this category -
let us say somewhere between 10 and 100.

Add that work on top of all the above and the 9 years
start to look less surprising.

Arne