Over on YouTube [The 8-Bit Guy] shows us how the TI-99/4A home computer worked.
[The 8-Bit Guy] runs us through this odd 16-bit home computer from back in the 1980s, starting with a mention of the mysterious extra “space” key on its antiquated keyboard. The port on the side is for two joysticks which share a bus, but you can find boards for compatibility with “newer” hardware, particularly the Atari-style joysticks which are easier to find. The AV port on the back is an old 5-pin DIN such as was typical from Commodore and Atari at the time (also there is a headphone port on the front). The other DB9 port on the back of the device is the port for the cassette interface.
The main cartridge interface is on the front right of the machine, and there’s a smaller expansion socket on the right hand side. The front interface is for loading software (on cartridges) and the side interface is for peripherals. The system boots to a now famous “press any key” prompt. (We know what you’re thinking: “where’s the any key!?” Thanks Homer.)
One curiosity is that when the system is waiting for a command the screen background color is a light blue, and when it’s running a command the background color changes to a light green. [The 8-bit Guy] demos some equation calculator software which has support for variables and expressions. In addition to the equation calculator the same cartridge has a version of BASIC (called TI BASIC) and a version of Space Invaders (called TI INVADERS). (Yes, the interface is all uppercase.)
When they were designing the system the TI-99/4A engineers had been considering an 8-bit CPU but they settled on the 16-bit TMS9900 instead. However, much of the board had already been designed for an 8-bit CPU, which lead it to being a bit of a weird hybrid. The CPU only has 15 address lines but it makes up for it by addressing two bytes at a time, allowing it to read up to 64K.
[The 8-Bit Guy] goes on to discuss the computer architecture, the Graphic Programming Language (GPL), and its various BASIC implementations. Also the internals of the cartridges are explored along with the Video Display Processor (VDP) which supported rudimentary graphics mode (32×24 characters with 15 colors and 32 sprites) in addition to a text mode (40×24 characters). The 4-voice sound generator chip was the SN76489, this chip proved to be useful in many other products as well.
[The 8-Bit Guy] finishes his video with a look at the expansion capabilities, which basically just daisy chain off the right hand side. Each of the peripheral devices demands its own power supply too!
If you’re interested in the TI-99/4A check out Persistence Pays In TI-99/4A Cassette Tape Data Recovery and Don’t Mess With Texas – The TI-99/4A Megademo.
Omg we used tot have ons of these. Came with some big box on the side too. I remember my dad sitting there hours to an end typing in code , by hunt and peck, (to this day he cant type properly)from a magazine, and surprised the game actually worked. I know I was in kindergarten at the time. Ah the memories.
I don’t want to be a troll but this reads like a Gemini generated summary of the video transcript, particularly the constant use of [The 8-bit Guy]. Please tell me Hackaday isn’t going down this path.
We are not.
Sorry about that. I find myself saying [The 8-Bit Guy] because I don’t want to guess at people’s gender… as for it reading like a transcript, it kind of is! My job is to give you a summary of what is in the article in case you don’t have time to read/watch the whole thing.
Appreciate your posting this … brings back fond memories. :-)
Honest question here, not trying to offend anyone. Would someone who identifies as female use a YouTube handle with “Guy” in it? Is that a thing? Or just force of habit?
Anyone who reads this.. you be you… just asking.
I thought wondering about pronouns was so 2023! Men are back to being men and sheep are back to being nervous!
If you don’t ask the question, then you should never assume.
This may seem like malicious compliance to make a point, but you should remember Poe’s law. The extremists who demand it cannot tell the difference between serious parody and compliance either.
why would you choose that image of all the available.
https://www.youtube.com/watch?v=eV0t4QIINLI
Why does HackaDay refuse to post a link to ‘Bill and Bill’s Gentleman’s Club’?
THAT was a brutal and apt burn.
I assume you’re talking about the thumbnail with a photo from an ad featuring Bill Cosby. I picked that because I thought it was fun! Haven’t seen Bill Cosby in a while! :)
Do you know why that is?…………..
It’s not a good reason… ;)
Nerds can be a bit clueless about pop culture, but jeez.
It’s kind of in poor taste, given what we know about Cosby. The guy was everywhere in the 80s and if he had been just what we all thought he was it would’ve been a fun throwback.
But he is a convicted serial rapist, with dozens of victims, and I think giving him visibility in this way is dismissive of that fact.
I don’t want to turn this into a whole thing, but I don’t want to ignore it either.
You apparently didn’t get the memo. Serial rape has totally been normalized, and coercing your secretary (or ChatGPT if you don’t have one) into sex just part of being manly man!
It’s entirely possible that the author of the piece was unaware of Cosby’s criminal history.
As of 2025, Bill Cosby is not a convicted felon.
It’s OK to go back to laughing at the ‘Spanish Fly’ bit on his early comedy album.
https://youtu.be/FH7uDNR_TBc?si=1cLG2JNMulQ_he6F
Oh dear, yes, I didn’t know!
What I wonder, is, how common this was behind the stage in general.
What if most celebrities had such dirty secrets, in general?
I mean, by the sheer number of fans they have/had it’s not too unlikely that they had affairs of all kind during their careers.
Blaming that one guy because had bad luck of being found out isn’t fair, isn’t it?
I mean, even officials and big leaders in human history that their dark stories..
Not that this is ethically right, but it’s nothing out of ordinary, I mean.
Yeah that sort of thing is pretty much par for the course for actors, directors, CEOs, politicians, etc. Power corrupts, and bad people rise to the top.
for the sprites you needed the extended basic cartridge. However when generating a memory overflow it was possible to somehow get those sprites working by loading values at some video memory. I thought it was rather strange that those sprites were already available on the machine without the extended basic cartridge. The user club was not interested in this discovery however
That sounds interesting! Do you have more info on this?
“for the sprites you needed the extended basic cartridge”
I bought one when they were $49 on clearance. Found that out and gave it away as a gift.
The photo in the article was not the 99/4A. It was the earlier 99/4 that had a chicklet-style keyboard instead of the true full-stroke typewriter keyboard that the 99/4A had.
^^^THIS
The 99/4A dropped the Equation Editor as well.
I used to do consulting for an oil-exploring organisation in Norway, programming a navigation computer for a survey ship. The computer used the available maritime navigation systems at the time (before GPS), i.e. Decca (passive and active), Syledis, Pulse8, and Loran. My program (running on an old HP computer) took the input from the different navigation systems and used the data from all of them plus data on pitch, roll and yaw to improve the precision of the position data.
Now to the tie-in to the article: the output from my program was sent to a TI-99 on the bridge and another in the computer room. The TIs showed the expected course as a curve on the screen and the current position of the ship so the captain or first officer could navigate based on that. The TI was chosen for its colour capability and because we had a guy who could program it.
(As an aside, we knew who was steering the ship just by watching how well the ship followed the expected course — the captain was way better than the first officer.)
Funny story!!
The photo is the original TI 99/4, with the “chiclet” style keyboard. The 99/4A had the “IBM Selectric” style keyboard. The console originally sold for $1000. When they were liquidating inventory they were selling in our TI plant for $25.
This was the first computer that I owned. As grad students, my wife and I couldn’t afford much, but when TI unloaded the last batch of these for $99, I went for it. I wrote assorted BASIC programs on it, calculating pi to a few hundred decimal places, running simple population dynamics simulations (with graphics, sort of), etc. But I had access to much more powerful computers at the university, so I didn’t do anything “serious” with it.
Parents got us one as teenagers. I got hooked on programming when I realized that the “DATA” statement in BASIC allowed me to input the actual ASCII values of the cubes in the game BOGGLE so I could generate believable BOGGLE letter layouts on the screen. So thanks, parents and TI, for launching my interest in technology. :-)
Did A.I. Write this? Serious question.
Where is the author’s personal voice?
And who decided that Bill the Abuser Cosby would be a good idea?
I went and checked out about 10 the other articles posted by the Author of this one, I don’t what it is about this one that sticks out as odd.
Maybe its just me but I didn’t find anything unusual in the voice, the 8 bit name or even the use of Bill Cosby in the print ads from that period. We’re talking about stuff that was around 45 years ago. You’ve all got to learn to roll with it, put it in context — you can’t go around ignoring the past just because it makes you feel uncomfortable. If you think this is weird try going back a bit further!
I quite liked the 9900 processor architecture but this ‘thing’ was obviously designed by people who’d only ever seen calculators. As the video pointed out there were plenty of more normal architectures around at the time, architectures that offered promises of real programming in languages other than BASIC.
Still have mine from the early teenager years. Works perfectly but sits up in the closet most of the time. :)
I used to wonder why it was always noted that “no machine language programming”. Sure they must be a way, intentional or not, to jump into user code.
Learning that only RAM on CPU bus were a 256 byte scratchpad, and the rest 16K was only accessible via the video chip through 2 registers made it clear. For the Basic interpreter (which itself was interpreted), I guess that was enough. Reminds me a bit of 1802 Basics, that used a virtual machine to run Basic. Maybe also Apple II’s Sweet Sixteen .
The TI-99 wasn’t supposed to have the TMS9900, its intended CPU wasn’t ready so they hurriedly shoved the 9900 in there where it didn’t really fit, hence the weird design.
Problem was the TMS9900 is meant for a minicomputer, hence the scratchpad RAM. For multi-user its great because you can swap out the registers as you switch between users. Doesn’t make much sense for a home computer.
TI didn’t want a little toy computer competing with its business computers (same CPU!), so they hobbled the design with 8 bit RAM, limited software etc. They also wanted strict control of software, even updating the TI-99/4A so it would lock out existing 3rd party cartridges.
So yeah, end result is a whole load of WTF. Had they stepped back and designed it properly around the TMS-9900 without the weird stuff, full 16-bit and not tried to lock out developers they’d have wiped the floor with everyone else.
That’s how I remember it, too.
Especially the part that TI initally didn’t want to support the electronic hobbyists/computer hobbyists.
Sometimes I really wonder what was wrong with those people making such decissions
and if it was mainly an US phenomenon to produce inferior products on purpose (“market segmentation”).
Because, where I live, the reputation of a company used to have priority over profits.
Building a loyal user base that lasts for a long time was more important than quick profits.
That’s why I struggle to understand this kind of business model, I guess.
To my understanding, the reputation, the legacy of a company is what matters in bad times.
Same way, it’s important to treat (and reward) the own employees very well.
Because if a company does that, the employees are more likely
to keep the company together and the work environment is much friendlier, too. They’re the very heart of the company, after all.
The most valuable thing the company has (besides the customers).
Happy employees will be much more likely to make valuable suggestions, too, if they’re not afraid of being laid off for having an own opinion.
Anyway, in case of TI it’s really not understandable why they made this decission back then.
If the original TI99 design truely was a rival to the mainframe business, who cares?
TI could have advertised the TI99 as a “mainframe for the desktop” and make software products that could exchange data between the TI99 and mainframes.
Or use TI99 technology to improve the big iron in mainframe business even further.
It could have been a win-win scenario if just interpreted in a positive way.
It could also be used to win new users for TI mainframes.
It really makes me wonder why US companies always did put so much effort into marketing and tricking customers
when they just could have played with open cards, be honest and produce good things.
Or are US customers slightly different than the rest of us, maybe?
Do they secretly want to be tricked by marketing slogans, pretty diagrams and popular actors? I seriously don’t know.
It just seems unlogical to me to produce something inferior just to be able offer “something” in a given market.
Because if it’s predictable that users will be disappointed,
the only conclusion that can be drawn is that they loose respect for said company, isn’t it?
Again, no idea what was wrong with those people.
If you can’t build proper airplanes that don’t crash land, then just don’t do enter airplane business? Right?
Really?
Let me point you to the German car companies.
They used to make good, but expensive cars.
Not for decades now.
They are good at ‘marketing and tricking customers’.
Keeping them coming back for yet another unreliable, bottomless money pit.
German car customers are stupid status obsessed twits.
Can’t blame Benz for taking suckers money, it would be immoral and unethical to let them keep it.
Not like the Germans think it can last forever.
They think cars are a dying industry anyhow and highest present value of the corporation is full tilt balls deep customer BFing, right now (no lube, just ghost peppers).
Like a big iron shop in 1980, the realistic ones think it’s all over but the end squeeze.
Know they can’t compete with new competitors, just from peter principle and their corporations age/high % senior people at level of incompetence.
It’s hard for many business to loot their own markets.
IBM’s PC business was kind of an accident…at that it didn’t work out great for them.
Look at the laughable electric cars coming from VW and Benz.
See also Kodak.
What happened to Agfa?
Are they dead or a digital camera company?
The simple fact is: ‘If you don’t loot your own business, someone else will.’
Hard to deal with, when nearly the entire hierarchy is working to hide the fact they are faking it.
Yeah! 😃
Just have a look at the company philosophies of Mr. Bosch here:
“I would rather lose money than trust.”
“I don’t pay good wages because I have a lot of money; I have a lot of money because I pay good wages.”
https://tinyurl.com/5n7wxrwv
I don’t remember that Siemens and Bosch had built poor tools or equipment on purpose back then (20th century, same century as TI here).
For example, the Bosch electric driller we have at home is from the 1970s and still works like new.
The Krups handy mixer from same time, too!
This used to be normal, before the 1990s.
Appliances and tools were supposed to last 10 years and beyond.
Modern German companies don’t count in my opinion (car industry etc),
they’re nolonger “German” by any means but just some random international companies.
Which have copied bad business practices so common internationally, sadly.
Telefunken, for example, now belongs to a Chinese company, I think?
It’s brand for Chinese TV sets, I think?
About modern German cars and manufacturers..
It’s a bit complicated, I think. The car companies still live in the past, I think, either by accident or because they’re still succesful
enough in their business by not changing.
Their research centers aren’t bad, though, paradoxically.
The prototypes shown at car fairs are quite promising.
Anyways, to our defense, at least the German cars made over here in Germany are rain-proof. 😂🥲
They’re being guaranteed to not rust from the inside to the outside. 😂
Sorry. Old joke.
Rain proof?
IIRC a certain vintage Porsche manual wished the owner ‘many sunny days’.
Also: Many new Benzes have the engine computer in the console.
So if you do leave the sunroof open, or it leaks, or you spill coffee, it’s a 10k++ bill.
Which is still better than VW engine computers under the wipers on the firewall.
So if you don’t clean out leaves, it floods.
First step to replace a ‘new Bug’ brake master cylinder?
Remove front bumper.
They’re laughing at their customers.
That said: Honda or Toyota. Pre 2014. Learn the car.
Not Ford, GM or FIAT.
German cousin has a nice Toyota 4×4 w electric truck nuts (blinkers and brakes…I might have wired them up).
I bet the other doctors are jealous.
Makes the patients extra secure, they’re in serious hands.
TI wanted the education market (losing to Apple in US & BBC in the UK). Start with the Speak & Spell, move on to the 99. Made sense. (I must say the TI-BASIC manuals were fantastic for learning programming.)
They weren’t interested in the tinkerers, and also didn’t want to cannibalize their business sales, plus had the IBM attitude of “everything is ours and you use it our way”.
They were smart enough to realize the money was in software, not hardware, but keeping such a tight grip on that aspect didn’t help them. They’re not alone in that of course.
They also wanted the machine released yesterday which was the icing on the cake,
Just corporations being corporate.
So the guys at TI opted to rather risk to alienate the whole professional user base, like Commodore did? 🤨
Is that really so clever? Because, from a customer’s point of view it might not.
AFAIK, In late 70s Commodore had its renowed PET line and tried hard to be a business company (-> CBM, as a play on IBM),
yet by early 80s they decided to make the mediocre VIC-20 toy computer.
Which then lead to the famous C64 (built using recycled VIC-20 parts) and created Commodore’s eternal reputation as a toy maker.
With a few exceptions, I mean. I don’t mean to be unfair.
The Commodore PC line gained some recognition, I admit.
Deutsche Bahn and some other gov. agencies had PC 10s and later models, I read.
Thats when CBM cosplayed as IBM, literally (IBM PC look-a-likes).
Sure, makes sense. The hobbyists and “nerds” who bought their TI calculators (TI Programmer etc).
What’s better than to exclude all those loyal customers by basically telling them they’re not welcome.
[..] in the US.
In my country,- at the time-, companies still had certain standards.
Profits weren’t everything. The founder and the family managing their company still had a say.
Thank you for the information, btw. 🙂
I didn’t know about the education sector.
I didn’t meant to say that TI was incompetent or something.
IT in its role as an IC and calculator manufacturer was fine, I think.
It’s especially the story TI99 that confuses me.
If IT aimed at education sector, then why didn’t it found a subsidiary or
create a real education computer based on schools’ or teachers’ needs?
To avoid harming the own reputation, I mean.
The TI99 was full of costly chips but didn’t even have a basic internal serial port by default. For an acoustic coupler.
If it had, then it would have been a nice looking serial terminal, at least.
Hi, speaking of TI-BASIC on TI99, it reminds me of the Thomson line of computers of the 80s.
The TO 7-70, TO 8 and 9 had advanced Basics on cartridges, too!
The overall look was a bit similar, too.
Or let’s use this analogy.:
If the TI99 was a piece of art, then I would ask myself “what did the artist mean to express?”
Likewise about markets and US companies.:
To me, it looks like a candy maker is suddenly trying to make rat poison.
.. because the new “market” must be entered and conquered.
The consequence that existing customers nolonger might buy candy
from same company (for obvious reasons) is happily being accepted as risk.
Seriously, what kind of business logic is this? 🤨
TI didn’t alienate business users, they already had them from their mini-computer stuff and they want to keep them there. Education was an entirely new and massive market. Then focus moved to the home, but back then it was well understood that computers were a bit too expensive for that. (That’s why Sinclair/Timex went really cheap.)
You have to remember TI invented all of this stuff, from the transistor (*) to the microchip to the CPU to computers to everything else, so of course they knew what they were doing, and they could do it better than everyone else, especially those little toy makers like Commodore or Atari, or those Apple hippies .
It’s just the usual arrogance, greed, short-sightedness and stupidity that companies do. It’s easy to see that in hindsight, but eh, it is what it is.
(* silicon transistor, Bell Labs did as well independently.)
Well not exactly. The TMS9900 used ram as the registers. To do that you needed fast static ram which was expensive at that time so that is why you only got 256 bytes of ram and then the rest was hung off the video controller. What is crazy to day made sense in 1979. It is true that they didn’t want to make it too good aka they didn’t want to eat the highend sales.
Not like they were the only ones. DEC could have made a PDP-8 pc cheaply about the same time but never did because the business market was to Profitable.
Holding the registers in RAM made sense in multi-user or process control, point to a different address and off you go as a totally different process.
It was a crazy CPU to use for a home computer, but they wanted to get the machine out the door ASAP.
Unfortunately, he made some mistakes in this video
Extended basic has both ROM and GROM and is mostly GPL with some assembly routines to speed it up..
Groms are 6K or 8K not 1800 bytes
Many people have expanded TI systems these days with the advent of modern side car systems like the tipi or the nano peb.. he grossly underestimates the amount of users out there for software.
He adds the speech synthesizer to the end of the expansion “train” which doesn’t work as the speech synthesizer requires the console for power. It has to be first..
He misrepresents the Homebrew pitfall homage program as an actual release from Activision
unfortunately some inaccurate info in there:
speech synth at the end of the train.. doesn’t work.. has to be first
grom size is wrong.. they are 6k not 1800 bytes
xb is not just assembly language, its also gpl some routines are in assembly
he’s misrepresenting pitfall as from activision when its a homebrew
he’s misrepresenting how many people have 32k and a drive capability
At one point, TI decided to give a complete system to all their senior technical people. The console, monitor, expansion box. Everything except games as I recall. They held a two hour training session on how to setup and use the system. Two hours for their best technical people! And this was supposed to be used by your average person? Who were a lot less computer literate than now. The cable to the expansion box could be plugged in 8 different ways. 7 of them wouldn’t work. I knew it was in trouble.
The video has a number of errors or omissions so you can tell it wasn’t produced by someone with a lot of experience.
The photo in this article is a 99/4 not a 4A (which replaced the chiclet keys with an actual keyboard). Also, an expansion chassis was available so that you could use cards instead of the sidecar style peripherals. There’s also a number of newer cards made after TI dropped it including USB, IDE, SCSI, an MFM hard drive controller, an interface to the raspberry pi, and a 1mb RAM card.
I worked on Logo for the 99/4 (and C64, Apple II, Mac, etc). The Sprite chip work had been done with a grad student in our lab and there was a deal with TI to come out with Logo. The 99/4 architecture had one big issue: all RAM except 256 bytes required 6 clock cycles to fetch over an internal serial bus. The 256 bytes were used for register windows in lieu of an explicit stack (BLWP instruction vs JSR from the PDP-11 instruction set) but Logo used some of it for subroutines that implemented fundamental data and control structures, in order to be fast. Mostly I worked on the last phase of the project with the TI folks, helping with source code questions, but I also proposed a version upgrade and implemented it, cross coding on a 9900 desktop machine, but alas the new version was not to be.
I went to work for TI in Lubbock in 1978, developing some of the original applications for the 99/4. However, my main contribution wasn’t the software, it was the music — as the only musician in the department (that’s how I got the job), I composed the original snippets of tunes that you hear behind most of the early programs. My favorite was the three-part composition I put together for the Demonstration program, a piece of which appears in the video. I don’t know many people have the opportunity to crank up a YouTube video and get to listen to music they wrote 47 years ago — but I gotta tell you, it was a thrill for me.
The “Demonstration” tune, BTW, was entitled “MJ”; I named it after a neighbor I had a brief crush on. MJ was a grad student at Texas Tech, and I don’t think she ever knew that she was immortalized in a tune that was probably heard by millions (OK, thousands) of computer geeks all over the world.
That computer that was pictured is a true 16bit personal computer unlike the other home computers that were around during that time.
In a design that was slower in BASIC than the 8-bits of the time.