"Strong typing vs. strong testing"

Martin Gregorie martin at address-in-sig.invalid
Sun Oct 10 21:09:35 CEST 2010


On Sun, 10 Oct 2010 21:38:11 +1100, Lie Ryan wrote:

> 
> Virtual Machine in Hardware... isn't that a contradiction?
>
Nope. Several mainframes did that. 

Two that I knew well were both British - the ICL 1900 and 2900. The 
Burroughs x700 series also used hardware virtualisation. Both Burroughs 
and 2900 series of machines could even run different addressing  and 
virtual hardware architectures, e.g. word-addressing vs. byte addressing, 
in each virtual machine. 

The 1900's  'hardware' registers, PC, CCR, etc were the first few words 
in each program's address space. That was late 60s tech, so scarcely a 
new concept nowadays. 

The ICL 2900 and, by extension Multics, since the 2900 hardware's process 
protection scheme was swiped from Multics, used a different approach - 
again hardware-implemented virtual per-process registers but in addition 
'rings of protection' which meant the OS could  affect your code but you 
couldn't touch it and the OS in turn couldn't touch the hardware drivers 
etc.


-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
org       |



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