[Info-vax] OT: IA-128 ???

[Bob Koehler]

In article <4ada755e$0$273$14726298 at news.sunsite.dk>, =?ISO-8859-1?Q?Arne_Vajh=F8j?= <arne at vajhoej.dk> writes:
> 
> I seem to recal that physical addresses of later VAX'es were bigger
> than 32 bit, but 40 bit sounds too much - that would be 4 TB of RAM.

   The VAX architecure was originally defined as 32 bits virtual address
   space - matching what is convenient to manipulate in 32 bit
   registers, and 30 bit physical address space - matching the 30 bit
   SBI on the 11/780.  After the 11/780, DEC made smaller, slower,
   cheaper models for a few years, and a couple other 30 bit models
   (11/782, 11/785).  Even when they build the 8000 series, they were
   either small models with the BI bus, or 86xx with 30 bit SBI.

   I don't know of any 30 bit SBI systems that offered enough options to
   use up all 30 bits.
   
   But when later systems approached 1GB RAM, I do recall DEC changing
   the architecture definition to have 32 bits of physical address
   space.

   You need at least several K to map usefull I/O adapters, so you can't
   really support all 32 bits of physical address space with a full 4GB
   RAM.

   But I don't recall VAX ever going beyond 32 bits physical address
   space.