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WTB: 286 to 386 / 486 Accelerator

coolmod121

New Member
Joined
Dec 10, 2020
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8
Been looking for a year now. Basically looking to upgrade my Teradrive PC from a slow low end 286 to a more powerful 386 or 486. Any help would be most appreciative!! Thanks!
 
Such an upgrade isn't really practical. I would at most aim for a 386SX because anything faster is a waste. A 386SX is similar enough to a 286 that upgrades that use it aren't terribly complex and it would likely be more compatible than a huge interposer full of GAL and PAL chips. The 386 SX isn't much faster, but it would at least give you 32 bit protected mode and allow you to run 32 bit applications.

Any 386/486 upgrade is going to be severely crippled due to the 286 bus. You're effectively hobbling full 32 bit CPUs (in the case of the 386DX and 486) onto a 16 bit data bus and 24 bit address bus. To make a bad situation even worse, the 286 has a multiplexed address and data bus, further slowing down an already slow system. And if that wasn't already bad enough, nothing on the motherboard side is going to run faster, so you're going to be stuck with the same 10 MHz 16 bit multiplexed system bus. Any time the CPU has to do out to the motherboard, it's going to be crippled and spend lots of time waiting for the system to give it something to do.

The Teradrive is also very RAM limited due to the upper address lines of the memory slots not being connected. The maximum amount of RAM it can handle is 4 MB. There is a mythical hack I've read about to connect the upper address lines and get more memory, but that's a big headache to do.
 
Such an upgrade isn't really practical.
I don't see why that matters, especially since there is no other way to speed-up that system. Also, many of these upgrades include L1 cache and double the CPU clock, so as for raw processing power, you can get quite a boost.

I have a Schneider Tower AT and been looking for such an upgrade as well.
 
Such an upgrade isn't really practical. I would at most aim for a 386SX because anything faster is a waste. A 386SX is similar enough to a 286 that upgrades that use it aren't terribly complex and it would likely be more compatible than a huge interposer full of GAL and PAL chips. The 386 SX isn't much faster, but it would at least give you 32 bit protected mode and allow you to run 32 bit applications.

Any 386/486 upgrade is going to be severely crippled due to the 286 bus. You're effectively hobbling full 32 bit CPUs (in the case of the 386DX and 486) onto a 16 bit data bus and 24 bit address bus. To make a bad situation even worse, the 286 has a multiplexed address and data bus, further slowing down an already slow system. And if that wasn't already bad enough, nothing on the motherboard side is going to run faster, so you're going to be stuck with the same 10 MHz 16 bit multiplexed system bus. Any time the CPU has to do out to the motherboard, it's going to be crippled and spend lots of time waiting for the system to give it something to do.

The Teradrive is also very RAM limited due to the upper address lines of the memory slots not being connected. The maximum amount of RAM it can handle is 4 MB. There is a mythical hack I've read about to connect the upper address lines and get more memory, but that's a big headache to do.


Oh I've already connected the lines needed for the RAM, but apparently it's limited in the bios as well, so I'm having a friend go over that :)

https://www.ebay.com/itm/333999239793 I made these for the teradrive as well seeing how that's another one of its short comings, but yeah...the CPU is a problem currently. I do have multiple 286--->486 accelerators, but the problem is they are rather long and don't fit in the teradrive in that particular orientation.
 
These are the ones I currently have (minus the top one as that's a 386 to 486BL3. Problem is they are all orientated where they slam into the riser card >.<
 

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Well if you could find the weird "male" PLCC connector, you could theoretically make an interposer to move/rotate the position of the upgrade board. Though I think you'd then run into a problem with height due to the bracket above and the ISA backplane.
 
Well if you could find the weird "male" PLCC connector, you could theoretically make an interposer to move/rotate the position of the upgrade board. Though I think you'd then run into a problem with height due to the bracket above and the ISA backplane.

Believe me, I've tried that. Even with proper support chips on the position board it didn't work. :(
 
Believe me, I've tried that. Even with proper support chips on the position board it didn't work. :(

Did you make a PCB interposer, or did you run bodge wires on like a piece of perfboard? I remember seeing another attempt at a 386 interposer, where the guy just used a bunch of bodge wires and it was super unreliable because it caused signal integrity issues. I'd think you'd have to make it a straight up interposer, rather than kicking it off to one side because that'd introduce trace length and noise.

With the relatively low number of pins, you should be able to do it in a 3-4 layer PCB. More complicated interposers, like the Evergreen 586 seem to only have 4 layers.
 
I did actually make a PCB interposer with the help of a friend. It was a no go, according to him the original PCB was already very noisy and introducing more with relocating it wasn't reliable.
 
That's interesting. Well you could always do like the guys over at 68kmla and roll your own upgrade board by reverse engineering. It'd give you an opportunity to clean the design up, quite a bit of work though.
 
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