I hesitate to go into the issues for lack of time, etc. I used to say 
that "HW is just SW crystallized early". The first computers didn't 
have index registers but did direct address modification. Some of the 
real disasters in personal computers were done because the hackers 
didn't want to use address spaces or the CPUs couldn't support them, etc.

Has no one noticed that graphics accelerators actually work? Etc. So 
HW choices make a huge difference.

The real question is: what is a really good computation model for the 
VHLL, and what of it could be made into special HW?

In my way of looking at objects and messages, they were supposed to 
be SW versions of how the ARPAnet and Internet were going to work: 
i.e. massive numbers, totally encapsulated, loosely coupled by pure 
messaging, and simultaneously active. Well designed hardware could 
make a huge difference on each of these compared to SW on a stupid CPU.

One of the several reasons we don't have a really decent OOPL today 
is the lack of suitable HW to run it.

The middle ground that was so successful at PARC which made up for 
the many things we didn't understand was the wonderful microcode 
architecture of the Alto and subsequent machines we designed and 
built. Today, FPGAs can fill some of this role.

Butler Lampson has estimated that today's architectures are about 
1000 times less efficient pound for pound than the Alto. That's 10 
doublings which equals 15 years of Moore's Law -- meaning that what 
can be computed today by all the straining, etc., could have been 
possible 15 years ago, and what we could do today will perhaps not be 
possible for another 15 years. This means that Moore's Law on a bad 
design doesn't make up for a good design of custom HW.

Just to pick one item -- suppose that instead of faking message 
passing with subroutine calls, the HW could enable real message 
passing. Or better yet, what if we could run a publish and subscribe 
with parameters matcher (like a modern version of LINDA) at the same 
speed as today's HW assisted subroutine calls? And what if these were 
between truly encapsulated objects that were the lowest level entity 
on the computer?

Cheers,

Alan

At 10:02 AM 5/24/2007, Ralph Johnson wrote:
>On 5/24/07, Alan Kay <alan.kay at squeakland.org> wrote:
>>Hi Ralph --
>>
>>I don't think either Ungar's architecture or the criticism of it
>>below address the most important issues of making VHL object-oriented
>>computer hardware (both then and now).
>
>I would be interested in knowing what issues you think are the most important.
>
>The thesis is Ungar's, but the architecture is not.  I think the
>architecture was a group project by Patterson's students.
>
>The point of the thesis is that a lot of proposed hardware features
>don't help performance very much, and in fact there are software
>solutions that are more effective.  This is a good point.  However, it
>doesn't mean that no hardware features can help.  Moreover, it assumes
>that hardware is expensive and software is cheap, and in fact the
>opposite is true.  People have been working on a JIT compiler for
>Squeak for some time, and we aren't using one yet.  It is easy to say
>"just put it in the compiler", but it might be too complex to ever get
>the compiler working.
>
>What do you think are the main issues?
>
>-Ralph Johnson