Yes. The VLSI 200 series chipset do exactly that

There are 386 and "486" upgrades for 286s that have clock multipliers. I have one that can even do 8x, but it's only useful in a 6MHz AT.
A 286 doubler is doable, but without cache almost useless.

Fastest 286 CPUs run at 25 MHz - in this case I would expect it to be 3 x ISA.

Anonymous Coward wrote on 2022-09-06, 03:45:

There are 386 and "486" upgrades for 286s that have clock multipliers. I have one that can even do 8x, but it's only useful in a 6MHz AT.
A 286 doubler is doable, but without cache almost useless.

Did I read that right? You are saying it is possible to put a 486 in a 286 mainboard?

Well, I did put "486" in quotes.
There are lots of manufacturers that made upgrades based on either Cyrix or or IBM 486SLC. I'm not aware of any upgrade modules that used real 168-pin 486s, but I own a Japanese Buffalo module that use the TI486SXL (386DX bus version). The only real benefit you get from using a 32-bit chip on a 16-bit motherboard is the 32-bit interface to the FPU.
286 upgrades could have been designed to take true 486 chips, but there was no market for it. The closet you can get (that I am aware of) is an ALR Powerflex with 486SX upgrade card. That was a 16-bit motherboard with 24-bit addressing, so while the upgrade was non-standard it kind of demonstrated the futility of such an arrangement.

Anonymous Coward wrote on 2022-09-06, 03:45:

There are 386 and "486" upgrades for 286s that have clock multipliers. I have one that can even do 8x, but it's only useful in a 6MHz AT.
A 286 doubler is doable, but without cache almost useless.

Why can’t this be modified for an AT?
It would clock the cpu independently of the bus

https://ctrl-alt-rees.com/2020-03-02-overcloc … -pc-sprint.html

Second, a 286-25mhz system with 1ws is said to perform nearly identical to a 286-16 worst case.

Why would a “clocked doubled” 286 perform significantly differently than one with a WS?

16 bit code rarely can take advantage of paging

286 can be adapted to 486 there are adapter boards. If you got that figured out perhaps a ti sxl2 could be shoehorned in…?

Hi! When I created the thread I was thinking about compensating the slowness of the 80286 somehow.
Things like slow bus interface unit or the cycles that certain x86 instructions need for decoding/processing.
Or calculating of 3D models and fractals. Such things, which are very CPU heavy.

What I like about the 80286 is that it was the last, most advanced 16-Bit x86 processor and that its front-side bus was the blue print for AT bus (aka ISA bus).

Using SRAM on the motherboard to increase performance might be more practical, maybe?
Having RAM at, say, 20 ns access time would be interesting. If the 80286 chipset plays nice.

(Speaking of, I remember the Sega MegaDrive/Genesis uses pseudo-SRAM as a substitute for real SRAM..
Not sure if that's still relevant, though. It just came to mind as an alternative.)

rmay635703 wrote on 2025-08-11, 16:03:

Why can’t this be modified for an AT? It would clock the cpu independently of the bus […]
Show full quote

Anonymous Coward wrote on 2022-09-06, 03:45:

There are 386 and "486" upgrades for 286s that have clock multipliers. I have one that can even do 8x, but it's only useful in a 6MHz AT.
A 286 doubler is doable, but without cache almost useless.

Why can’t this be modified for an AT?
It would clock the cpu independently of the bus

https://ctrl-alt-rees.com/2020-03-02-overcloc … -pc-sprint.html

There are probably at least two dozen different dinguses that exist to upgrade a 286 CPU. The most basic one I’ve seen was a clock doubled 386sx with no external cache. I’ve never owned this model, but I read that without cache the clock doubling provides almost no benefit. The main point of the upgrade was to get 386 memory management.

I think the easiest path would be to clone one of the 486SLC upgrades.

Jo22 wrote on 2025-08-11, 21:40:

Hi! When I created the thread I was thinking about compensating the slowness of the 80286 somehow. Things like slow bus interfac […]
Show full quote

Hi! When I created the thread I was thinking about compensating the slowness of the 80286 somehow.
Things like slow bus interface unit or the cycles that certain x86 instructions need for decoding/processing.
Or calculating of 3D models and fractals. Such things, which are very CPU heavy.

What I like about the 80286 is that it was the last, most advanced 16-Bit x86 processor and that its front-side bus was the blue print for AT bus (aka ISA bus).

Using SRAM on the motherboard to increase performance might be more practical, maybe?
Having RAM at, say, 20 ns access time would be interesting. If the 80286 chipset plays nice.

(Speaking of, I remember the Sega MegaDrive/Genesis uses pseudo-SRAM as a substitute for real SRAM..
Not sure if that's still relevant, though. It just came to mind as an alternative.)

The 386sx was a 16-bit processor as well.

I thought about SRAM to replace DRAM some time ago... You can technically put SRAM on sticks and use latches to be compatible with DRAM, but you don't gain anything because the bus clock and the memory controller are the bottleneck. You'd have to redesign the motherboard and connect SRAM directly to the CPU with your own 'controller' to address the SRAM. You can technically have full speed cache & RAM in one with zero wait-state, but what does that open the door to application wise? What can you do now that you couldn't before...

MikeSG wrote on 2025-08-13, 16:56:

The 386sx was a 16-bit processor as well.

That's not true. It's a full 32 bit design internally, with 32bit memory addressing and registers.

The difference to the DX is that the SX external interface was chopped down to a 16bit data bus and 24bit address (hence the lower limit of 16MB of RAM). In all other aspects it's identical to the DX.

It's where on the (rare) SX motherboards with cache (or really aggressive memory timings) you can get an impressive speed up.