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

[Joseph Huber]

P. Sture schrieb:
> 
> RSX-11 could address more than 16 bits to support extra RAM, but I 
> forget the details.
> 
No, all, even the high end 11/44,11/70,11/73,11/83 had 16 bit addresses.
What You may have in mind was mapping 16 bit addresses to 18 or 22 bit 
RAM space through an MMU: 8 segments of 8KB size of the 16 bit address 
space were mapped at any time to some part of the RAM. This is usually 
called segmented virtual addressing.
The total memory addressable for a program was still 16 bit = 64KB.
Some PDP models have 3 address spaces (Kernel,supervisor,user) each 
64KB, but not at the same time; i.e. a change of mode had to occur to 
access one of the other address spaces (either interrupts,traps,or the 
CMS instruction "change mode to supervisor").
Some models had separate I(nstruction) and D(ata) address spaces: 
programs built with I/D mapping could address 64KB I space (instructions 
and immediate data), and 64KB data at the same time. So with some right 
one could say they have 17 bit addressing.

-- 

  Joseph Huber   - http://www.huber-joseph.de