[Info-vax] Kittson question

[David Froble]

JF Mezei wrote:
> On 15-01-06 19:52, Stanley F. Quayle wrote:
> 
>> You can't "pretend" to be a MicroVAX 3100 but emulate a VAX 4000-600.
>> Emulate a MV 3100 and quit pretending.
> 
> SimH has instructions on how to change a couple of bytes in the "ROM"
> file to change the model number. Changes nothing to the emulator, only
> what the booting OS sees as the hardware type.
> 
> Microvax II may be special case since many instrctions are emulated and
> I beleieve sepcial shareable images are loaded. But once you get to full
> VAX models, are there really differences in how VMS operates ?

JF, I think you may be missing something important.

A HW emulator is just that.  It takes a HW instruction, and performs it 
in software.  Even if it's a MVII emulated instruction, that instruction 
emulation is still a set of instructions, which the emulated VAX performs.

For example, if looking at the difference between the instructions 
supported on a MVII and some other VAX, the only difference is that some 
instructions may not be supported in HW, and the OS then emulates those 
instructions.  It does so by executing a set of instructions to prform 
the same task.  Regardless, the HW emulator just executes instructions.

The VAX instruction set is just that, the well defined HW instructions. 
  Now, if someone is implementing a HW emulator, there would be no sense 
in emulating just those instructions a MVII, for example, would support. 
  It would be much better judgement to emulate the full set of VAX 
instructions.  One emulator that can do everything a VAX can do.

Now, the HW emulator can have some data identifying some particular 
model for licensing and other reasons.  Without those special reasons, a 
VAX is a VAX is a VAX.  From a design perspective, there can be only one.

Hope this helps a bit.