@UsagiElectric on YouTube has a series of videos on building a homebrew around the TMS9900 processor. Would be cool if a unix-like OS could be used on something like that, though sounds like this project is specifically targeting the TI-99/4A system.

The TI-99/4A was the first computer I owned as a teenager. I had used TRS-80s and Apple ][ at school. I eventually bought the expansion box and a couple of accessory cards (floppy disk drive, memory and RS232). It all went in the e-waste dumpster about 20 years ago during a move.

I had one in grade school. Taught me the value of backups early in life. Spent all night typing in a game from a magazine. Started it without saving to tape first. It was so loud! Panicked and restarted the machine. Sadness ensued.

Replaced it with a C128-D. Didn’t get my first intel until I bought a 386 after graduating high school. Good times.

Can you drop this yt channel name?

you only get 3 guesses

Same here - parents bought one for me in 1982, IIRC. By 1984 I had moved to Atari XL, but I'll always have a soft spot for the TI-99/4A, Extended Basic cartridge, speech synthesizer, cassette drive, etc.

My sister and I used to co-type programs from "Compute!". The times were so much simpler then..

The TI99/4A was my first computer when I was 7 or 8. Unfortunately, no cassette drive. As soon as I shut it off, my basic program was gone!

The TI99/4A was also my first computer. I was about 5, and I didn’t really seriously try writing programs until I was about 8. Fortunately, since my father bought this for work, we had a large collection of peripherals, including the floppy disk drive. Unfortunately I learned the hard way why my father stopped using it: peripheral expansion bus devices were exquisitely sensitive to static shocks. I remember reeling in horror after watching hours of work just disappear from the disk drive. I suppose this was probably a good lesson to learn at an early age!

HOLY COW. Thank you for this. I LOVE the Ti99/4a, its one of the first computers I ever used. I've got one up and running at home now currently and can't wait to try this.

Btw, there is a lovely third party replacement for the TI99/4a video chip that lets you output VGA. It’s a major life improvement if you are seriously using it. I Dremeled my case but you can route the ribbon cable to avoid it if you’d prefer not to modify anything. Happy to send you a link if you don’t already know about it.

Thanks! I've got mine running in to a 9" Pelco PVM and it works well but yea, its tiny. I'd love to plumb in VGA and use a 15" flat panel. Would love a link.

It's the first computer I ever programmed, I was twelve years old then. <3

This is the main updated comment with the user guide and download

https://forums.atariage.com/topic/380883-unix99-a-unix-like-...

Thanks. I wasn't looking forward to browsing all those pages in the hopes of finding the source. Did they never put it up on GitHub?

Wow. The TI-99 is such a perfect fit for this too given the chip was designed for multi-user computing in a way other home computer chips weren’t.

All due to TI’s desire to use the same chip standards across all their machines big and small, IIRC.

While the CPU is a better fit than the 8 bit contemporaries, the 16kb of working memory is going to be a struggle.

It's cool because the registers are all in RAM, with a "workspace pointer" on the CPU pointing at where they are. This is slow, but a context switch is just changing that pointer.

Well, it has 256 bytes of RAM which is basically a really big register file, and everything else goes in the 16kb of "video RAM" which you can read and write by poking at I/O registers. So it is not easy to program.

It's arguably the only 8-bit computer which has a really different architecture from the others. You could otherwise imagine pulling the SID chip off a C-64 and putting it on a TRS-80 Color Computer etc.

Sharing the main RAM with video was a weak point in computers of that time period because the video system stole many of the memory access cycles. Some recent retrocomputers that revisit that period like

https://www.c64-wiki.com/wiki/Commander_X16

have a full-size memory bank and a video RAM memory bank which is accessed through a port which can be pretty efficient because you can auto-incremement the address register and just write 1 byte to the port to write 1 byte to video RAM and repeat.

Yep, but it lacks a MMU so memory protection and paging are going to require a lot of work. I think the only reason this is feasible at all is they're running the OS out of a ROM cartridge.

The PDP machines that Unix was developed on had MMUs, which they needed because the 16 bit processors couldn't address the multi-megabyte address space the hardware supported.

I'm pretty sure the Centurion doesn't run Unix.

Did the minicomputers of the time have MMUs?

I thought UsagiElectric showed a case where his Centurion didn’t, but I may be misremembering.

I learned to program on this exact hardware in the early 80s as a small child. It uses BASIC. It's hard drive was modem tones recorded to an analog audio tape. Its monitor was an analog TV. There was no mouse. The keyboard was built into the computer itself.

So assuming one wanted to buy a used one of these (I had timex sinclairs around this time) how would one display the composite video nowdays?

A USB video capture device or a converter box. There are devices sold specifically to interface these old machines with modern displays. One of the more famous ones is the RetroTINK.

The joy of computing still lives in the age of AI...

Does it run PARSEC? Nice shot captain!

made me remember knightOS

https://github.com/KnightOS/KnightOS

WoW!

Imagine a Beowulf cluster of these.