Incidentally, I picked up a pair of AMD 286 16/S chips recently. A few months ago I pulled my A,T&T 6300 out of storage for a cleaning and noticed that it is actually a 6300 Plus, which is a 286 based machine. My hope is that it can be upgraded with one of the 16mhz AMD chips and an oscillator swap. The 286 chip used in these is of the type shown on this page

http://www.chipdb.org/img-amd-r80286-16-s-sma … l-logo-5637.htm

and has to be held in place by the heatsink which is clipped down. It is not held in place by friction. 286 chips of this type maxed out at 16mhz as far as I know, unless someone wants to correct me on that. I haven't ever seen a 20 or 25 of that design, but maybe someone else has.

We need news of this system. And benchmarks would be awesome.

carlostex wrote:

We need news of this system. And benchmarks would be awesome.

I wish I had the time. Also, the barrel battery was old and dead but doesn't seem to have leaked. The system still boots, so thats a good sign but I can't locate an exact replacement for it. I unwrapped it and it's just 3 button cells inside but no markings on those so I have no idea if I can even build a replacement barrel battery. I also don't know if the crystal controls only the CPU speed or if other parts are dependent on it. I don't want to put a faster crystal in and have the CPU work only to fry parts elsewhere on the motherboard, parts that would likely be irreplaceable after so long.

^ I didn't know you had a 25MHz 286 too. My shout was at Jolaes... And i agree, don't crystal mod your 286 if the jump is too big.

My project was interrupted some time ago just before encasing the components but I think I can squeeze in a few quick benchmarks tomorrow or on the 14th.
I wanted to put a 2 MB S3 805 VGA card in it that I bought from FGB not so long ago (an excellent card, btw) but unfortunately this card is incompatible with 2 MB RAM in this system.
I do not know why but it works only when 1 MB RAM is installed (which I will not do) so I will return to the Tseng 4000. I do not have that card with me at the moment so I can only run CPU / mem / HDD benches.
The S3 805 will serve well in a 386...

Nice.

Is the S3 any faster than the Tseng?

No, it was generally slower in a 386 but it is way more compatible when dealing with not-so-standard resolutions.

Unfortunately, I am having DMA problems now on the motherboard with AHA 1542CF cards so I cannot connect SCSI disks 🙁
I forgot to take notes about the system the first time it worked - about the exact config, slots occupied, Memory installed, CMOS settings etc.. so now I need to dig up a very old, small IDE HDD to cross-check the HDD DMA issue. I really hope that it is not the Citygate chipset that crapped out on me...

Small photo update.

Still investigating the SCSI DMA problem. Will need to try other SCSI controllers.
Old, small capacity IDE drives seem to work. I got an ST-1144A brick sized 125 MB HDD that does freeze the system. Works even when the BIOS settings are maxed.
I have currently 1MB DIP and 2x4 MB SIMMS installed, totalling in 9 MB 70ns RAM.

I also had to change an all-OK 6V external battery for a 9V alkaline to keep the CMOS settings. Maybe this board needs a 9V or 12V battery... I do not have the specs.

A Yamaha YMF 719-BS is also installed - no DMA problems with this one. At this speed, sound can come up garbled in some games, though (e.g. Wolfpack)

You should run 3D Bench and Speedsys as well. Is that FPU runing synchronously? A 287 running at 25Mhz could be a recipe for trouble.

To my best knowledge, it is running at about 17 Mhz but somehow comes out misreported because of the BIOS settings.

3D Bench is pointless with this lowly Trident 9000c - I cannot get home for the Tseng ATM 🙁

Are you sure that Speedsys runs on a 286 ?

Not sure but speedsys can run in real mode. In theory a 286 should run it.

carlostex wrote:

You should run 3D Bench and Speedsys as well. Is that FPU runing synchronously? A 287 running at 25Mhz could be a recipe for trouble.

There are no 287 rated for 25mhz operation. 20mhz is the fastest I've ever seen, but those are like hen's teeth. They''re even harder to find than the 25mhz 286 itself.

20mhz is the fastest I've ever seen, but those are like hen's teeth

then I feel extra lucky. Recently I have bought a box of old hw for about 42 USD. A price with a meaning, isnt it 😀 Among a few exotic cards and boards there was a Fox II rev 3.4 board with a 20 Mhz Harris AND a 20 !!! Mhz IIT math coprocessor. All working perfectly, without a glitch... I wonder how much it would go for on ebay... but no, I just gotta keep to this rare find for a while 😀 Especially because the Headland chipset supports EMS emulation, so no EMS board is necessary. This is really a killer combo for a 286 system.
I need to check the actual running speed of the copro yet.

The system in this thread has what appears to be an Intel 287XL running at 25MHz. Can it handle that speed? Though it is based on 386SX core, Intel never rated it higher than 12.5MHz.

I let the factory test and bench suite run for about 2 hrs and it did not fail. I have not run productive stuff like CAD, spreadsheet utils etc. on it.

m1so wrote:

And Harris 286 25 Mhz is an awesome retro gaming machine. It pretty much runs smoothly any DOS game that does not use memory over 640 KB.

My 286-16 has 4Mb Ram.
A 286 can Adress up to 16Mbytes of RAM, if your Board can handle it.
So there is no Problem running Programms requiring more Memory then 640Kb.
If i want i can have up to 3,3Mb EMS Memory, or 3Mb XMS on my Machine, or a Piece of Both at same time.

It runs Wolfenstein and Spear of Destiny well.
Wing Commander 1 runs too.
Even Ultima Underworld runs at Medium. With Sound it becomes very sluggish. Its very good optimized it needs only about 2Mb Ram.

I can even run Big Programs on Windows 3.1, i run C++ Builder 3.1 from Borland and old Version of JASC Paintshop Pro.

All these reminders of all my unfinished projects. I still have to test if the Cyix 287XL+ I bought a while back works. I know there's some fakes out there but I only paid a few dollars for this one, so it's no big loss if it doesn't work.

Wow! I've been looking for a board with that CPU for a while, but they are so rare. Would it be possible to buy a more common 12MHz 286 board and swap out the CPU? I found a seller selling the CPU itself (68-pin PLCC), but would I also need to swap out the oscillator?

I need to find my 286 boards again, they are in a box somewhere.

I have a super fast 286 board with an Intel 286 12 MHz. I also have a 48 MHz crystal to replace the 24 MHz one and a Harris 25 MHz CPU, I have just not mated the three yet.

Im pretty sure this combination will be really really fast at 24 MHz if everything works out, with luck even fast enough to rival some members Harris 286 overclocks at ~30 MHz. The BIOS lets you change pretty much every timing there is but defaults to pretty slow settings with the ISA bus running at half the CPU speed. I think replacing the CPU and doubling the speed with a 48 MHz crystal should be more or less hassle free.

The question is how agressive settings I can use when everything is running at twice the speed. With the 12 MHz CPU I can set every timing and other setting to the fastest value and run the ISA bus in sync with the CPU.

My plan B is a PC Chips M209 motherboard that uses a Harris 20 MHz CPU at the moment. This board would probably do close to 30 MHz but I'm pretty sure the other board will be faster even at 24 MHz.

I also have an Intel 287XL I orderd from China a week ago incoming. Not the fastest 287 CPU clock for clock but at least they can handle high clocks should some motherboard try to run it in sync with the CPU.