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From: John Ames <commodorejohn@gmail.com>
Newsgroups: comp.os.linux.misc,alt.folklore.computers
Subject: Re: The "Good" Old Days - Complete Specs for DX-10 Operating System
Date: Wed, 2 Oct 2024 09:15:02 -0700
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On Wed, 2 Oct 2024 03:18:23 -0400
"186282@ud0s4.net" <186283@ud0s4.net> wrote:

> The 990 series used the TMS-9900 chip and near variants. This was an
> odd chip - kept the CPU registers out in ordinary RAM and could
> switch quickly between different sets of registers. At that time, the
> external RAM and CPU kinda ran at the same speed so little was lost
> putting the registers in RAM.
> 
> I remember fooling with this chip on a TI-99/4a home computer (which,
> tragically, horribly under-used the neat new 16-bit CPU). There were
> ASM commands for dealing with the register, 'context', shifting. By
> that means many users with their own space could be implemented
> directly with the hardware.

I've always found the 9900 concept interesting, although its core
assumption about memory speed doesn't really hold up today; much of the
architecture was eventually reincarnated in TI's MSP430 series micro-
controllers, but they ditched the memory-resident register file. But
for the time, context-switching certainly didn't get any faster than
that; only three actual registers to save, but you still got a
comfortably PDP-11ish environment from the programmer's perspective.

But yes, it's astonishing just how bad the TI-99 design was; a cascade
of bad decisions that turned what could've been a real contender in the
home-computer wars into an absolute joke. One of my oneathesedays
projects that I've toyed with for years (though never made any headway
on) is to roll up a homebrew system that does right by the concept...

> How it is now AIN'T how it always was.

And may it never be forgotten ;)