[Info-vax] nice for VMS

[Richard B. Gilbert]

JF Mezei wrote:
> Bob Koehler wrote:
> 
>>    There are a variety of states related to memory management, including
>>    PFW, COLPG, and others I could dig up somewhere.
> 
> But virtual memory management is under the responsability of the OS. But
> waiting for 8 bytes of physical memory to be loaded into a the register
> is very much hardware based and would the OS be aware of this operation
> taking a long enough time to warrant a switch processing to another
> process ?

If your memory is aligned properly; e.g. the three low order bits of the 
address are 0, a load of 8 bytes should go quickly.  If they are not 0, 
the O/S will do its best which, admittedly, is not very good.  ISTR that 
it must move the eight bytes to properly aligned temporary storage and 
then load them into a register!  This takes many cycles longer than a 
properly aligned quadword load.  The compilers know how to do it right 
but if you use Macro and fail to align things properly, your code may 
run like a dog!