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Rare XT with Rarer CPU

Trixter

Trixter

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Chicagoland, Illinois, USA
(Moderators: Before you move this to the "for sale" forum -- I'm not offering this for auction, I just saw it and thought people would like to know about it.)

If I weren't broke, I'd bid on auction 250157865367 over at ebay -- it's an IBM 5162, which is the 6MHz 286 model they produced for one year. It's one of the more uncommon PCs from IBM. What makes this one interesting is that 1. opening bid is one dollar (normally ebay stores with vintage goods try to soak you), and 2. according to the pictures, the CPU was replaced with a Kingston 386/25SX piggyback accelerator board.

That's a pretty rare find, so hey, have at it.
 
Hmm a 386sx with 640K or 1MB RAM, how usefull is that?

Is the 286/6mhz that rare? Any idea how many were made?
 
The memory may be limited, but you can still atleast execute code faster.

Perhaps with Expanded Memory you could get more memory, and do something interesting like Doom, but I would imagine it would be very slow.
 
Unknown_K said:
Hmm a 386sx with 640K or 1MB RAM, how usefull is that?

Is the 286/6mhz that rare? Any idea how many were made?
Click to expand...

The 286/6mhz cpuis not rare at all. The XT/286 I read somewhere that about 20.000 should have been made.

You'd need an expansion card for extended memory than 16 meg should be possible (anybody offering one, pm me :) )
 
Wait, is expanded memory available on a 16-bit interface? I thought they were only 8-bit interfaces, which would actually slow you down.

(not only that, but would this particular machine with the 386 upgrade only be addressing memory at 16-bits then instead of 32-bits?)
 
evildragon said:
Wait, is expanded memory available on a 16-bit interface? I thought they were only 8-bit interfaces, which would actually slow you down.

(not only that, but would this particular machine with the 386 upgrade only be addressing memory at 16-bits then instead of 32-bits?)
Click to expand...

Expanded memory (EMS) is always slow, because of the 16/64K page swapping technique it uses.
Being a 286, this machine should be able to use extended memory (XMS) if you place a memory expansion card (like for instance AST made).
As EMS was developed due to the adressing limitations of the 8088/8086, those cards will be 8 bit ISA normally. XMS cards I would expect to be 16 bit ISA, as they do not work with XT class machines.

The XT-286 also has two 30 pin SIMM slots. I have no idea what happens if you put two 1 MB SIMMs in there- I do not dare to try it in mine.
 
Well, I do believe in its stock form, the XT/286 will not recognise more than 512kb installed in the SIMM slots (but don't quote me on this). However, I believe I have seen mention of people making modifications to allow use of 1MB SIMMs.

@Evildragon

Yes, there are such things as 16-bit ISA cards that can provide expanded memory as a secondary feature, but I am not aware of any stand alone 16-bit EMS boards. You would probably want EMS hardware available for a 286 system since they aren't capable of emulating it.

...and, 286s do 24-bit memory addressing and 16-bit datapath. The 386SX chips are similar in that regard. If a 386DX were plugged into a 286 socket (I happen to have a module like this), it would function exactly as a 386SX. Oh, and one interesting thing about that Kingston 386SX upgrade module...I believe that AUSTEK chip also contains 8kb of L2 cache. In this case the memory datapath is probably less of an issue than the fact that the CPU is running at 25MHz, but the rest of the system only at 6MHz...so access to memory will be slooooow.
 
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Trixter said:
(Moderators: Before you move this to the "for sale" forum -- I'm not offering this for auction, I just saw it and thought people would like to know about it.)

If I weren't broke, I'd bid on auction 250157865367 over at ebay -- it's an IBM 5162, which is the 6MHz 286 model they produced for one year. It's one of the more uncommon PCs from IBM. What makes this one interesting is that 1. opening bid is one dollar (normally ebay stores with vintage goods try to soak you), and 2. according to the pictures, the CPU was replaced with a Kingston 386/25SX piggyback accelerator board.

That's a pretty rare find, so hey, have at it.
Click to expand...



/grin

/want

/bid
 
Even with the speedup processor, the system is not likely to be nearly as fast as a true 386 system. The RAM in a 386 system is likely to be somewhat, if not significantly faster than the RAM in the XT/286. The XT/286 is using 150ns memory, a real 386 system is probably going to use 80ns memory. The 386 would have to insert more wait states to compensate for the slow memory. I approximate that 8 wait states would be required for the 386 to access the memory on the XT/286 board. Memory on Extended Memory Boards could be a lot faster, but for conventional memory you are limited to what is on the motherboard. At least you wouldn't need Expanded Memory Boards anymore, EMM386 and the like would take care if that.

Would the speed of the system be reflected in the speed of the onboard devices, the 8237 DMA Controllers, 8259 Interrupt Controllers, 8254 Timer, 14686 RTC, the 612 DMA Page Register, and the 8048 Microcontroller? Do the speeds of those devices increase as the processor speed increases beyond 8MHz?
 
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Ah, RNS auctions. I have had luck with them, awhile back I bought a Macintosh Classic and a 100FT cat5e cable off of them, and shipping was fast. I'm still debating on whether or not I should bid.

--Ryan
 
Is the piggy back CPU thing supposed to have a 286 CPU in the socket too? In those pictures, it doesn't, notice how the socket is blank, and the camera doesn't show the whole board...
 
I have a working IBM XT-286 motherboard that I got awhile back in a box of
motherboards I bought on eBay. I think I was lucky to get this :) The seller had it listed as an AT motherboard. Eventually I'll get around to finding a case to put this in, I have all the parts I need to build a working system, but no case. I found lots of great pictures of this motherboard at this link (click on the More pictures link):

http://www.yesterpc.com/Hardware/ISA motherboard/IBM XT286/item.htm

Luckily I also had a pair of those old 9 chip SIMMS to install in the board,
not sure if it will work with non-IBM SIMMS.

The XT-286 motherboard uses an external battery, just like the AT. There's a battery connector
next to the keyboard plug. So I would think battery acid corrosion on the motherboard could be a concern
just as it is with the AT.
 
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From my experience with a Make-it-486 adapter, the upgrade modules don't really speed things up much (even with clock doubling and 1kb L1 cache), but having the 386 memory management is really nice. Not to mention, with that adapter you can use a Fasmath 387 chip, which would be a hell of a lot faster than a crappy 287 (unless you have an XL).

Now what would be really interesting is if you installed a TI486SXLC2 clip-on adapter on top of of the kingston module...then you could have 8kb of L1 cache AND 8kb of L2 cache. That might give a decent speedup...but who knows if it would actually work.
 
Trixter said:
Doom is unplayable on any 386 under 33MHz. And you need to hit F5 while it's running to make it low-res to get a decent framerate. Just FYI.
Click to expand...
I knew that, it doubles the pixels thus rendering less detail (the Sega 32X does this for Doom, and that's ALL you get sadly)
 
Jorg said:
Expanded memory (EMS) is always slow, because of the 16/64K page swapping technique it uses.
Click to expand...

Common misconception. It's actually faster than XMS in pretty much all implementations because XMS requires copying the data in/out of 640KB. With EMS, you simply swap pages, and can then reference the memory directly (ie. no copying). True, some EMS implementations are less efficient than others, but if the programmer isn't a moron, EMS is always faster.
 
Great Hierophant said:
Even with the speedup processor, the system is not likely to be nearly as fast as a true 386 system.
Click to expand...

That's not why I posted; I posted because it was an uncommon find, not because it would be the speed of a true 386 (it wouldn't).

Would the speed of the system be reflected in the speed of the onboard devices, the 8237 DMA Controllers, 8259 Interrupt Controllers, 8254 Timer, 14686 RTC, the 612 DMA Page Register, and the 8048 Microcontroller? Do the speeds of those devices increase as the processor speed increases beyond 8MHz?
Click to expand...

Not usually, no.
 
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