[Info-vax] OpenVMS.Org quick pool

[Johnny Billquist]

On 2012-08-24 04:49, Johnny Billquist wrote:
> On 2012-08-23 22:28, Stephen Hoffman wrote:
>> On 2012-08-23 18:05:57 +0000, Johnny Billquist said:
>>
>>> No point. You cannot address more than 64K with a PDP-11, so even if
>>> you had 1 MB, you could not address it.
>>
>> You're referring to the 16-bit addressing design of the PDP-11, most
>> likely.
>
> Indeed.
>
>> Later PDP-11 systems support 22-bit memory addressing.
>
> Yes. But the PDP-11 compatibility mode/AME under VAX didn't do that.

Oh. I should probably point out that "22-bit address" is the physical 
addressing of the machine. Virtual addresses are always 16 bits, even on 
modern machines with 22-bit physical addresses.
And since AME only offers user mode PDP-11 compatibility, you will only 
ever get virtual addresses...

The same deal with split I/D-space. AME, as well as PDP-11 compatibility 
mode on those VAXen who had that, never supported split I/D-space, not 
supervisor mode (or kernel mode), or anything else beyond a very 
simplistic PDP-11, barely enough for running usermode code of the 
simplest kind.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol