286 mod?

[monzamess]

Anyone know what's going on here? Seller says unit has a 286 mod of some sort... I don't plan to spend $210+s/h to find out.

https://m.ebay.com/itm/IBM-PCjr-with-fl ... SwZKRbO~1v

Edit: I assume this is the Reddit post mentioned in the listing:
https://www.reddit.com/r/IBM/comments/8 ... t_this_is/

[Brutman]

I believe it's the same machine; the person from the Reddit thread was quite clueless about what it was.

I wouldn't pay too much for it though; it's basically a pile of parts as the person doesn't know enough about it to say anything more than that it boots. Unless you are going to try to reverse engineer it to make another one, you are better off with just getting a real 80286 based system.

(Years ago I would have killed for something like this. You will note that it's been languishing on eBay for a few months now.)

[monzamess]

Thanks, makes sense. I got the impression it had been there a while but I'm too dumb (and/or impatient) to find the listing date on eBay's mobile interface.

[jharre]

It appears that the 286 is in that small box atop the jr and attached with 2-conductor lamp cord wire. Huh?

If that's the case, I can chop up an old P4 motherboard, attach it the same way, and have a Pentium 4 powered PCjr!

Or, wait!! There's probably an old i3 floating around here somewhere.

Am I missing something?

<*> Jim

[Brutman]

Look at the origial Reddit pictures.

There is a ribbon cable going into the system unit. The lamp wire is probably just for power.

[jharre]

Ah! I see. Just looked at the eBay pix earlier - now see what you mean.

[OldComputerGuy]

I saw that, too. I was not able to find any information about any 286 upgrades that were ever advertised or released. It seems pointless to me, though, because it looks like you'd be mounting a 16-bit chip on an 8-bit bus which would cripple it severely. Having to access memory beyond 128k indirectly through the sidecar bus instead of directly would cripple it further AND having it mounted in an external box instead of on the motherboard would likely introduce another performance bottleneck. Any software written to specifically support the PCjr video modes probably won't support the combination of PCjr video and the newer features of the 286 CPU, either, since it never came with one. It looks like it would be a nightmare trying to figure out how to get this hodge podge to actually work without any sources for documentation of the upgrade.

Edit: It looks like it's an ISA 286 upgrade board for either a Tandy 1000 or IBM PC mounted in an external box. If it's a homemade hack, there won't be any documentation to be found unless the original creator comes forward.

[jmetal88]

I saw that, too. I was not able to find any information about any 286 upgrades that were ever advertised or released. It seems pointless to me, though, because it looks like you'd be mounting a 16-bit chip on an 8-bit bus which would cripple it severely. Having to access memory beyond 128k indirectly through the sidecar bus instead of directly would cripple it further AND having it mounted in an external box instead of on the motherboard would likely introduce another performance bottleneck. Any software written to specifically support the PCjr video modes probably won't support the combination of PCjr video and the newer features of the 286 CPU, either, since it never came with one. It looks like it would be a nightmare trying to figure out how to get this hodge podge to actually work without any sources for documentation of the upgrade.

Edit: It looks like it's an ISA 286 upgrade board for either a Tandy 1000 or IBM PC mounted in an external box. If it's a homemade hack, there won't be any documentation to be found unless the original creator comes forward.

Sounds like there wouldn't really be much of a gain over a V20 installation plus speedup mod.

[OldComputerGuy]

So which one of you guys ended up buying it?

[monzamess]

Not me!