TI-99/4A

From: Ross Archer <archer_at_topnow.com>
Date: Wed Jan 31 04:24:45 2001

Corda Albert J DLVA wrote:

> I always thought the TMS9900 was a neat chip (having a PDP-10
> background may have influenced me :-) Having the register set
> show up in memory gave me a nice warm nostalgic feeling. I
> wouldn't blame the poor performance of the 99/4A on the CPU. The
> architecture had a lot of nifty things in it. Most of the blame
> for the poor performance of the 99/4A falls on the low-end
> save-every-penny-you-can design criteria for the machine.

I've always had a weakness for those huge 64-pin DIP CPUs. :)

Amazing what passes for cost-cutting then vs. now. I took a
TI 99/4A (dead on arrival) apart and discovered a wealth of
fastening screws, RF shielding, really thick PCB material,
hand-wired jumper wires, and a pretty respectable keyboard
inside, that you just wouldn't find in a low-end product today,
but apparently they went to heroic effort to cut silicon costs.

Fast forward to 2001, and cost cutting means as little metal,
as few fasteners, and the cheapest mechanical build possible,
flimsy thin PCB material, and stuff that might fly apart if you pull
the case off, but yet no problem with adequate RAM, ROM,
or silicon. :)

Am I the only one who thinks mechanical design cost-cutting has
finally gone too far? I almost forgot that stuff was once
this well put-together.

-- Ross




> I
> ordered the technical manual on the 99/4A from TI... What
> I saw in the manual made me gag... aside from a very small amount
> of memory actually on the system bus, any add-on RAM was
> accessed _serially_ (i.e. 1 bit at a time) via what TI called
> a "CRU" interface (basically a high speed serial port) I
> believe we can all appreciate the crippling effect on any
> machine's performance when the bulk of it's memory is only
> available through a 1-bit serial interface.
>
> BTW, I also had the technico board... a really neat product that
> never quite took off. :-(
>
>
>
> > -----Original Message-----
> > From: ajp166 [mailto:ajp166_at_bellatlantic.net]
> > Sent: Tuesday, January 30, 2001 8:30 AM
> > To: classiccmp_at_classiccmp.org
> > Subject: Re: TI-99/4A
> >
> >
> > From: Ross Archer <archer_at_topnow.com>
> > >
> > >Correct me if I'm wrong, but I've heard the 99/4A suffered
> > something of
> > >an unfair rap for being slow due to the fact that its TI BASIC was
> > >dreadfully inefficient and sloppy, and that little or no
> > blame for its
> > >slowness rested on the actual CPU or hardware. (Windoze
> > >users may spot a parallel here.) >;)
> >
> > Partially correct. there were many issues. One the 9900 is
> > 16bit wide
> > data bus demuxed to 8bit (costs a lot of cycles!, penalty 1),
> > it's run at
> > less than maximum speed for the time and BASIC {internal} was
> > interpreted as an end language {penalty 2} and the BASIC interpreter
> > was interpreted {penalty 3}.
> >
> > Those things really hurt speed. The other side was it did have one of
> > the better from a capability standpoint Basics in the
> > standard console.
> >
> > >The TMS 9900 CPU actually used a "window" in RAM as its
> > register space,
> > >with an internal pointer register to locate its base
> > address. This was
> > >actually a great idea at the time, because CPU cycles were
> > long enough
> > >back then it made no difference whether you stored temporary
> > values in
> > >internal registers or external RAM, as either could get you
> > your data in
> > >the 1 cycle time available.
> >
> >
> > Actually many of the older DEC hardware also used part fo ram to
> > implement the registers including early PDP11, DEC-10s and previous
> > machines. The idea was not new and was to save logic in the CPU
> > as FlipFlops (memory) were costly in hardware back then and even in
> > late 70s were costly on silicon. The other factor is the 9900 was
> > a single chip recreation of the TI990 mini (not unlike like the
> > 6100{pdp-8}, LSI-11 and DG MicroNova).
> >
> > >(And interrupt latency can be really short if you can make a "fresh"
> > >register bank with one register load!)
> >
> > The ability to context switch fast was one of the strong points.
> > Compared
> > to Z80 or 8086 it was a nicer cpu to program save for the 32KW memory
> > limitation. In many respects it was more similar to the minis like
> > PDP-11
> > or Nova than the micros of the time. It was rich in general
> > registers,
> > Addressing modes and IO.
> >
> > I have a Technico Super starter board and it runs the TI9900 at 4mhz
> > with 16bit wide memeory and rom really fast compared to the Z80
> > (comparison made on both machines I still have from 1979!).
> > I picked up
> > the TI99/4a and was sadly disappointed save for the bundle of
> > really good and inexpensive software for it. Still, it plays
> > a mean game
> > of
> > Parsec!!!
> >
> > Allison
> >
Received on Wed Jan 31 2001 - 04:24:45 GMT