[HN Gopher] UNIX99, a UNIX-like OS for the TI-99/4A
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UNIX99, a UNIX-like OS for the TI-99/4A
Author : marcodiego
Score : 114 points
Date : 2026-02-23 20:05 UTC (2 hours ago)
(HTM) web link (forums.atariage.com)
(TXT) w3m dump (forums.atariage.com)
| glimshe wrote:
| The joy of computing still lives in the age of AI...
| Zardoz84 wrote:
| WoW!
| b00ty4breakfast wrote:
| made me remember knightOS
|
| https://github.com/KnightOS/KnightOS
| haunter wrote:
| This is the main updated comment with the user guide and download
|
| https://forums.atariage.com/topic/380883-unix99-a-unix-like-...
| bink wrote:
| 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?
| MBCook wrote:
| 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.
| jandrese wrote:
| While the CPU is a better fit than the 8 bit contemporaries,
| the 16kb of working memory is going to be a struggle.
| MBCook wrote:
| Yeah it really was an interesting choice on their part. Makes
| sense as a move for TI. Not the target market.
| SoftTalker wrote:
| 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.
| jandrese wrote:
| 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.
| MBCook wrote:
| Did the minicomputers of the time have MMUs?
|
| I thought UsagiElectric showed a case where his Centurion
| didn't, but I may be misremembering.
| McGlockenshire wrote:
| In fact the 9900 itself was used in an entire line of
| minicomputers that included a hardware memory map.
|
| The 9900 is a single chip implementation of the CPU board
| in the TI 990. They even created a dedicated memory
| mapper chip to go along with the product line, though it
| is significantly different than the one in the
| minicomputer line.
|
| (edit: the 990 was first built in the early 70s, memory
| mappers are quite old conceptually)
|
| (edit 2: in fact the necessity of using a memory mapper
| is what killed the platform, and was one of the things
| that made the IBM PC team decline the 9900.)
|
| Unfortunately I don't think that there is a reasonable
| way to perform real hardware-level memory protection with
| that chip alone. I'm working on a project documenting the
| genesis of the 99000 chips, which include a privilege bit
| in the status register, from the minicomputer line.
|
| Essay forthcoming, and probably an OS. Maybe a year...
| jandrese wrote:
| 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.
| PaulHoule wrote:
| The PDP-10 had an MMU similar to a modern MMU with page
| tables and such, the PDP-11 had an 8-segment-of-8kb MMU
| like what the TRS-80 Color Computer 3 had except the
| PDP-11 had a real supervisor mode and if a user mode
| program tried to change the MMU configuration it would
| fault.
| PaulHoule wrote:
| 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.
| bananamogul wrote:
| Imagine a Beowulf cluster of these.
| SoftTalker wrote:
| @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.
| ectospheno wrote:
| 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.
| hn_acc1 wrote:
| 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..
| icedchai wrote:
| 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!
| raddan wrote:
| 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!
| sunanda35 wrote:
| Can you drop this yt channel name?
| Brian_K_White wrote:
| you only get 3 guesses
| mikestaas wrote:
| TI-99/4A was my first computer as well. I still have two of
| them, and they still work as well as they did in the '80s. I
| graduated to an Apple ][GS which I still have as well, although
| it needs some TLC before attempting to boot it so as not to let
| out the magic smoke.
| davepeck wrote:
| My parents bought one for the house when I was in elementary
| school. I still remember the sound of the Speech Synthesizer,
| excitedly discovering 20 GOTO 10, and playing Hunt the Wumpus.
| I eventually asked Santa for a C64 and spent some formative
| years learning 6510 assembly and mucking with the SID chip.
| buildsjets wrote:
| Does it run PARSEC? Nice shot captain!
| nonamenoslogan wrote:
| 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.
| raphar wrote:
| It's the first computer I ever programmed, I was twelve years
| old then. <3
| raddan wrote:
| 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.
| nonamenoslogan wrote:
| 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.
| UncleOxidant wrote:
| 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?
| jandrese wrote:
| 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.
| nonamenoslogan wrote:
| I'm using a Pelco 9" PVM that had a former life as a security
| camera monitor. Suprisingly good video for composite, but alas
| its not very large.
| hunterpayne wrote:
| 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.
| arnonejoe wrote:
| For some reason I was thinking it was that $99 dollar Sinclare
| from the 80s which had the most unusable keyboard on earth.
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