[Info-vax] Running Alpha VMS under the ES40 emulator

[johnwallace4 at yahoo.co.uk]

On Saturday, 5 October 2013 20:45:03 UTC+1, Scott Dorsey  wrote:
> Simon Clubley  <clubley at remove_me.eisner.decus.org-Earth.UFP> wrote:
> 
> >On 2013-10-04, Keith Parris <keithparris_deletethis at yahoo.com> wrote:
> 
> >> On 9/27/2013 5:26 PM, Simon Clubley wrote:
> 
> >>> As I mentioned previously, I use 32-bit versions of Linux at home.
> 
> >>> The kits previously mentioned all require either Windows or 64-bit Linux.
> 
> >>
> 
> >> So your Linux is 32-bit. Are any of your CPUs 64-bit? I found that using 
> 
> >> VirtualBox on a system which had an x86-64 CPU but which was running a 
> 
> >> 32-bit OS I could use VirtualBox to emulate a 64-bit CPU and thus run a 
> 
> >> 64-bit OS under VirtualBox under a 32-bit OS.
> 
> >
> 
> >Interesting. I will keep that in mind.
> 
> 
> 
> Linux did an okay job of handling the x86 64-bit transition.  Not as good
> 
> a job as Solaris did, but a lot better job than Windows did.
> 
> 
> 
> 32-bit code will run just fine on 64-bit Linux systems.  It may take some
> 
> fiddling to figure out what libraries need to be installed, since not all
> 
> of them for every application come by default, but it's not a huge deal.
> 
> 
> 
> It can be a pain building 32-bit binaries on 64-bit systems, and it can
> 
> be an adventure at times because the 32-bit and 64-bit libraries have the
> 
> same names but different paths.
> 
> 
> 
> But, overall, there is no reason to run a 32-bit Linux if your hardware
> 
> can support 64-bit mode.  These days you might as well just go with the
> 
> 64-bit kernel by default.
> 
> --scott
> 
> -- 
> 
> "C'est un Nagra. C'est suisse, et tres, tres precis."

Don't know whether readers are all aware, but in AMD64 mode, you gain not just a wider virtual address, which may or may not be a winner, but you also gain twice (roughly) the number of CPU registers, and a few other new featurettes. Twice as many registers is frequently useful, as any PDP11 assembler programmer (or compiler author) will tell you.

So a program that doesn't need a 64bit VA *may* get a performance gain simply because it has more registers to play with. On the other hand, in 64bit VA mode, pointers etc take up twice as much cache space. It's not always a guaranteed win to switch to 64bit mode, though it frequently is.

Apologies if I'm repeating myself here.