[Info-vax] Emulation Performance

[Simon Clubley]

On 2013-01-17, David Froble <davef at tsoft-inc.com> wrote:
>
> Consider (as far as I know) what an emulator does.  We throw around the 
> phrase "emulate an Alpha" or whatever.  But is it really emulating an 
> Alpha?  Now I'm guessing, and would enjoy reading any corrections, that 
> the hardware is NOT emulated.  What's happening is that the instructions 
> are emulated to give the same result, from the instructions, that the 
> hardware would give.  But what about Out of Order, pipelines, and some 
> of the rather esoteric stuff done in CPUs.  It's my guess none of this 
> is present, so the performance from such features is lost even before 
> getting into the overhead of emulating the instructions.
>

The hardware can be considered to be emulated, as long as you realise the
hardware is far more than just the CPU. CPUs are generally treated in the
way you describe, but all the devices (controllers, I/O ports, etc) are
emulated at the device register level and you need a accurate model of
how each device works in order to be able to achieve that.

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
Microsoft: Bringing you 1980s technology to a 21st century world