[Info-vax] CRTL and RMS vs SSIO

[Stephen Hoffman]

On 2021-10-24 14:34:35 +0000, Simon Clubley said:

> As I and others have told you from the beginning, getting VMS code 
> running on another operating system is not easy.

If OpenVMS app were uniformly easy to port, VSI itself wouldn't exist.  
Many of the easier-to-port apps have already been ported, too.

BTW, for those following along at home, including those considering 
porting OpenVMS or other apps to Windows, the 26† drive letter "limit" 
mentioned else-thread recently hasn't been an issue for a while; not 
since somewhere around Microsoft Windows 2000.

https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-2000-server/cc938934(v=technet.10) 


Windows picked up hardlinks support back then, something OpenVMS has 
also seen added.

The whole of the device name abstraction with the device driver 
"prefix" that's used on OpenVMS is another artifact of RSX-11 and 
VAX-11 era I/O bus configuration processes. It likely wouldn't be used 
in a newer operating system design, and OpenVMS itself mostly moved on 
from the whole construct with the advent of file-based configuration. 
And then there's the whole host name and allocation class cluster 
"prefix" ($) that got added a while back. This device-naming stuff is 
also indirectly tied into the logical name processing hiding in the 
lower realms of the OpenVMS I/O subsystem, too. Parsing the resulting 
device names—something I'd prefer to never have to do—within 
filenames—something else I'd rather not have to do—as part of scanning 
I/O configurations or devices or clusters—yet more I'd rather not 
contend with—got ugly, too. And this gnarliness also all gets more 
interesting to port, too. But I digress.

As for SSIO, the "fun" with that was always that first pesky S; around 
corruptions during shared file access.

And looking at SSD speeds now at DDR3-1066 RAM speeds and at main 
memory running at on-die LLC cache speeds from ~five years ago make me 
wonder how long many existing app assumptions around memory hierarchies 
and memory latencies will continue to be useful.

Fun times.


†Technically, it's arguably 24 devices and not 26, as A and B 
reportedly cannot reference HDD/SSD storage. Not that I've ever needed 
or tried or considered remapping A and B, given that links can and do 
work.



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