Storage and 25 MHz options for 286

[tonism]

I probably can crystal mod it, but the whole idea of my builds have been to see how fast things go per factory specs. Basically drop-in replacements and don't really wan't to go into overclocking.

IMO you should try the xtal swap anyway. The SCAMP chipset was only rated at 25MHz in 386 applications sure, but that doesn't mean it won't work with a 25MHz 286

It feels too much out of spec of what I'm trying to do. It pains me to leave this board, but I think I need a factory-rated 25 MHz 286 board to have a restful sleep at nights

These things seem to be as rare as Alaris Cougar board I managed to get hold on for my next project.

[tonism]

I was browsing the TH99 286 motherboards and came to realization that I basically have two options for building my 286 (if I do not want to crystal-mod it):
1) 25 MHz with 4 MB of RAM
2) 20 MHz with 16 MB of RAM

Now granted, 4 MB is plenty enough for 286 and extra 5 MHz affects all situations. But its not that the 20 MHz lacks in the speed department and Windows is never satisfied with enough RAM.

So, could the 20 MHz 286 with 16 MB of RAM actually be the better machine? Or am I just trying to justify my Biostar motherboard and making up excuses now?

[Svenska]

But its not that the 20 MHz lacks in the speed department and Windows is never satisfied with enough RAM.

If you are thinking of Windows 3.1, then 4 MB are plenty. Most applications which can make use of more memory use 32-bit instructions and won't run on a 286. I've tried.

There is not much software out there which would benefit from more than 4 MB of memory. Basically, it boils down to a large disk cache (which you don't want to make too large, otherwise flushing takes too long) and a ram disk.

I'd say: Go for the 4 MB device with 25 MHz. It's plenty.

[tonism]

I was afraid of that I guess I keep my eyes open for 25 MHz board then.

If someone happens to have some leads, I would really appreciate that.

[maxtherabbit]

hold on a minute - if you can manage to find DRAMs fast enough to run the 20MHz system at 0ws it will be superior overall than a 1ws 25MHz machine (my understanding is 25MHz at 0ws is not plausible)
does your biostar support 0ws? my 12MHz biostar board does

additionally there is EMS to consider for DOS, you will probably want to break out at least 2MB of your main memory to reserve for that
AND Windows 3.11 runs great on a fast 286 with lost of extended memory. It will absolutely benefit from >4MB

[Svenska]

That is a valid argument; I did not consider the wait states. The additional 5 MHz in clock speed are useless if the CPU spends them waiting for memory. This is actually more important than memory size as well.

I second the point on EMS support - software which can use it will benefit, and 286 machines cannot emulate EMS in software (like 386+ can) - but some 286 chipsets contain EMS support. If you can get 1-2 MB of EMS in addition to 4 MB of XMS, you should definitely go that route. I think Windows 2.x can use EMS as well.

On the other hand, I'd rather say that Windows 3.1 works well on a 286, but not particularly great (Windows for Workgroups 3.11 won't run at all). And while it can definitely use more than 4 MB of memory, you will also find that many larger Windows applications - which would benefit from a lot of memory - simply won't run (e.g. Microsoft Works 3.0 won't work, although Works 2.0 does). Those older, smaller applications are less likely to benefit from additional memory as well and games tend to run in DOS anyway. Of course, multi-tasking will benefit, but any 286 is going to struggle with it.

[maxtherabbit]

That is a valid argument; I did not consider the wait states. The additional 5 MHz in clock speed are useless if the CPU spends them waiting for memory. This is actually more important than memory size as well.

I second the point on EMS support - software which can use it will benefit, and 286 machines cannot emulate EMS in software (like 386+ can) - but some 286 chipsets contain EMS support. If you can get 1-2 MB of EMS in addition to 4 MB of XMS, you should definitely go that route. I think Windows 2.x can use EMS as well.

On the other hand, I'd rather say that Windows 3.1 works well on a 286, but not particularly great (Windows for Workgroups 3.11 won't run at all). And while it can definitely use more than 4 MB of memory, you will also find that many larger Windows applications - which would benefit from a lot of memory - simply won't run (e.g. Microsoft Works 3.0 won't work, although Works 2.0 does). Those older, smaller applications are less likely to benefit from additional memory as well and games tend to run in DOS anyway. Of course, multi-tasking will benefit, but any 286 is going to struggle with it.

my 0ws 286 @ 15MHz with 10MB RAM runs Win3.11 notforworkgroups pretty damn well (12MB total but 2MB carved out for hardware EMS)

[dhau]

I tried AMD 287-10 as FPU, but it was too unstable. Makes sense if the second crystal is for that.

287 socket has a pin that switches how fast your 287 chip works. By default it should run at 2/3 of your CPU frequency, so for CPU at 20 MHz you need an FPU that is rated for 14MHz+. Unless your board has jumper to switch between 2/3 and 1x modes and it is set to 1x.

I am using Intel 287XL FPU in my Harris 20MHz board and it works fine.

[tonism]

This is how the BIOS options look like. I really should disable the mem check and ticking sound now when I finally got the 16 megs of 60ns RAM that seems to work without problems. I guess the Global EMS Control means I have BIOS-level EMS support and just need a driver now? Perhaps someone has a good suggestion for this.

287 socket has a pin that switches how fast your 287 chip works. By default it should run at 2/3 of your CPU frequency, so for CPU at 20 MHz you need an FPU that is rated for 14MHz+. Unless your board has jumper to switch between 2/3 and 1x modes and it is set to 1x.

I am using Intel 287XL FPU in my Harris 20MHz board and it works fine.

Thanks for confirming. I actually ordered the XL as well, waiting for arrival.