[Info-vax] Itanium CPU configuration conundrum

[Michael Moroney]

VAXman-  @SendSpamHere.ORG writes:

>Two, supposedly, identical Integrity 6600s.  One, however, reports that it
>has 4 sockets filled with quad core CPUs while the other claims 4 sockets 
>with dual core CPUs.  

>HP says they don't have quad cores.  Strangely, VMS fires up and it says
>that it is starting CPUs #1 through #15.  Is its console and what it is
>reporting to VMS horked?

The Itanium zx2 chipset has a duplicate set of registers that can enable
it to switch between processes very quickly (by switching register sets).  
VMS knows about this and implements it by treating the second register set
as a second CPU, if some magic bit is set, making each core into two
virtual CPUs.  So, a two core chip can appear as either two or 4 CPUs to
VMS.  In reality, there are still two cores, and a given core may spend
half its time as one CPU and half the time as the other CPU, so
CPU-intensive jobs won't execute any faster.  There are probably some
situations where enabling this can cause a speedup.  Supposedly the VMS
scheduler has enough smarts to schedule two processes on different cores
rather than the two virtual CPUs on one core if it can, as this is 
obviously faster.

I believe SHOW CPU/FULL will identify the virtual CPU pairs somehow.

It appears that the magic bit got set on one 6600 and not the other.