TI 990 architecture / was Re: TI-99/4A Floppies - test-drb@ccmp.vtda.org

3 Oct 2007

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Subject: Re: TI 990 architecture / was Re: TI-99/4A Floppies
   From: "Liam Proven" <lproven at gmail.com>
   Date: Tue, 02 Oct 2007 20:18:00 +0100
     To: "General Discussion: On-Topic Posts Only" <cctech at
classiccmp.org>

On 02/10/2007, Allison <ajp166 at bellatlantic.net> wrote:

  The 9900 chips is not crippled, for 1976 three
voltage NMOS its about as fast
 as the technology of the time could go.  The TI99/4 did however do a nasty to
 it. One is they muxed the bus down to 8bits wide and that does slow the system
 some. There were 128 words of ram (6810s) that if you execute there the speed
 is noticeable.  The other is the GROM (sort of an interpreted language with a
 register point to next instruction) is a bottleneck as well.  There was a
 later 9980 and the 9985 which were a 8bit bus interface and were somewhat
 crippled but I'd never seen one in a TI99/4A. 
That's probably true, but the 99/4a wasn't a 1976 machine. It was
released in 1981 and withdrawn 1983. A bit unfairly for a tweaked 1979
machine (the 99/a), the 99/4a's competition was mainly 1982 machines
like the Commodore 64 and Sinclair Spectrum, which (based on my
possibly erroneous recollection) outperformed the 99/4a significantly. 
...
 The TI99/4 did however do a nasty to
> it. One is they muxed the bus down to 8bits wide and that does slow the system

I requote the statement.  Why?  Because thats what I'd said.  The basic 9900 
chip was fairly fast the 99/4 computer is _not fast_ and I gave the reasons why.
Comparing it to 1980 tech just showed how badly the little console faired.
Having a 9900 system without the funky 99/4 hardware I can say the 9900 was
still not fast but faired far better against its contemporaries.  The reason 
it did well enough is the archetecture was very good even if 2mhz was somewhat 
slow.

Allison