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stynx
August 3rd, 2014, 10:43 AM
Hi, i have modified several accelerator cards für 8088-based PCs. My first try was with 286 accelerators (Orchid TwinTurbo, Breakthru,...). I have archived good results in terms of speed. Some Boards could reach 20mhz with new sram (15ns) and a 25mhz-class Harris 286. I replaced the 286 with a 386sx CPU replacement Board which i upgraded to a IBM486SLC2 with 50Mhz. All these Upgrades were fun, but all games and programs would be limited to 640k. I tried to expand the memory by using an UMB-Card (128k) but that will not help to get past the 640k barrier. A better solution had to be found. The Intel Inboard was just the thing i was looking for. The optional 2 or 4mb of Memory would give me the the means to play some advanced DOS-games on an 1984 PC XT. I bought my 1st Inboard and ... no expansion :-( ... why not modify the thing until i get an expansion? I upgraded the 386DX16 to an 386DX33 and clocked the board to 25mhz. I replaced the 387 with a 487 and later the 386DX with a TI486DLC then with a TI486DLC2. Recently i have received another Inboard, this time with the 2mb Expansion :-D. In DOS DOS4/GW automatically identifies the Inboard and configures Games and programs to use the XMS. 2mb is a bit limited 4mb or more are needed. Therefore i analyzed the Memory daughter board and have a (nearly) complete pinout of the 2 40pin expansion-connectors. It turns out that the expansion-connector will support 8mb of memory... in a near perfect PS2-module compatible way. A 2-banked 8mb 72pin memory module should be perfect and only 5 support-ICs are needed to interface the module.
More details are found here:

286 accelerator for the original PC XT (http://forum.classic-computing.de/index.php?page=Thread&threadID=4892)

Intel Inboard pinout (http://forum.classic-computing.de/index.php?page=Thread&threadID=6526)

Its in german but the pictures and files should talk for themselves ;-)

stynx
January 3rd, 2015, 02:04 AM
Current layout of the Inboard 386 8mb memory expansion card in development... there will be some modifications, but the signals and pinouts seem to fit.
22016

Chuck(G)
January 3rd, 2015, 09:34 AM
I think that it's worth noting that at least here in the US, XT-type accelerators were pretty uncommon. One reason was the ascent of clones--mostly from Taiwan--and the 5170-class machines that offered much more power than the lowly XT.

stynx
January 4th, 2015, 05:35 AM
I think that it's worth noting that at least here in the US, XT-type accelerators were pretty uncommon. One reason was the ascent of clones--mostly from Taiwan--and the 5170-class machines that offered much more power than the lowly XT.

It was the same here in Europe. You could easily get a new cheap clone mainboard from taiwan with a 10 or 12mhz 8088, 286 or later even 386 CPU cheaper than a similar accelerator. Most people just bought a new PC when they got cheap enough (less then 800DM = about $300 in 1988). There were a lot small electronics shops here in Germany (even 3 in our little village) that could get you these and install them in your computer. The hardware wasn't expensive, the installation was ;-)

The Inboard and similar accelerators were more or less niche products and i can't really say where this niche even was, maybe the portables? I have 4 different kinds of accelerator boards (8088->286, 8088->386, 286->386, ...) and several replacement cpu-upgrades but all these are indeed very rare.

-Jonas

krebizfan
January 4th, 2015, 05:44 AM
The Inboard and similar accelerators were more or less niche products and i can't really say where this niche even was, maybe the portables? I have 4 different kinds of accelerator boards (8088->286, 8088->386, 286->386, ...) and several replacement cpu-upgrades but all these are indeed very rare.

-Jonas

The accelerator's niche was large companies that had strict approval processes for a new computer but any expansion card was automatically accepted. Money was wasted and the accelerated system still had to be retired quickly as newer software wouldn't run on the accelerator.