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

[George Cornelius]

johnwallace4 at yahoo.co.uk wrote:

> 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.

So, for arrays of pointers, or code with lots of 64 bit
memory references, it can be costly.  But a 64 bit processor
may have more cache; and ability to address beyond 4 MB can
be a huge gain, and more so as time goes on, with more and
more applications just don't cope well with a memory
constraint of that sort.

I'm finding that what it takes to almost completely freeze
up my 512 MB / 32 bit Linux system is to leave Mozilla up
overnight with multiple tabs open.  It pagefaults for what
seems to be a full 15 minutes at that point, and may still
be nearly unusable when it all unfreezes [OK, using an
external Seagate USB3 drive on a USB2 port for paging -
spinning at an unspecified RPM - but you get the picture].

George