segmented memory models

Jim Brain brain at jbrain.com
Mon Aug 4 00:56:42 CDT 2008


Roy J. Tellason wrote:
> On Sunday 03 August 2008 22:57, Jim Brain wrote:
>   
> specific devices.  Not likely applications.  Or were they handling their own 
> I/O?
>   
I think, at the time in Intel history, I would not fault the designer 
for assuming there was no OS or there was no guarantee an OS would be 
calling the shots.  I'm not sure of who was first (MOS, Moto, Intel, 
others), but I know the 6502 did not assume an OS, and I think the 8080 
was a bit older than the 6502.
> I found the 8080 (but more so the z80) to be of some interest,  but porting 
> all existing apps to newer chips never made all that much sense to me,  
> considering the other differences besides the CPU chip.  More available RAM, 
> a lot more standardization of system architecture,  a lot more common 
> standard hardware,  and all sorts of other stuff.  It was no surprise to me 
> at all to see lots and lots of newer apps and I don't recall seeing all that 
> much that got ported over,  or at least not that much that I knew about.  And 
> yet that backward compatibility seems to have been an issue for a lot of the 
> designers for some reason.
>   
Even today, when we design a new X, it's very important to ensure that X 
is backwards compatible with X-1, even though we are sure that few will 
care.  I would go so far as to label designs that were not backwards 
compatible (without good reasons) with the moniker we're discussing 
here.  Note that the designer ensuring backwards compatibility is not 
the same as encouraging it.  Still, it's drilled into a designer's 
head.  Don't break compatibility unless there a *VERY* good reason.

Jim



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