[Info-vax] Virtual memory 101 (was Re: Android development...)

[JF Mezei]

On 14-09-23 21:30, Stephen Hoffman wrote:

> On VAX and Alpha, the change-mode operation — an instruction on VAX, a 
> PALcode call on Alpha — triggers what is called an exception, and the 
> exception is then received and processed by the system service 
> dispatcher, which looks at how it was called, and (it's a dispatcher, 
> after all) dispatches to the system service.

So basically, the mode switches from user to either exec or kernel only
when the process executes a particular opcode that triggers that
exception, and the exception is granted or rejected based on where the
instruction is located in memory ?

Is this grant or reject decision  properties given to the page of memory
containing that code ? Or is there a page range that defines system
space, and that range is specified in hardware specific physical memory
location ?