The OS/2 Museum sometimes seems to have a knack for acquiring hardware so obscure that it cannot be even identified. One of the more recent arrivals was a seemingly typical Baby AT 286 board with an 8 MHz CPU. The board was in remarkably good condition for its age, having been produced in 1986; the date code on the PCB could be read as 15-98 or as 86-51, but there’s no question which of the two interpretations is correct. A significant contributing factor to the good shape of the board was no doubt the fact that it uses a CR2032 lithium coin battery and not one of those horrible leaky NiMh rechargeables.
The board claims to have been made in Japan by a company named Fujitech, or maybe Maxware. Interestingly, a very similar Fujitech XT board was seen with a sticker on it referencing Octek, a Taiwanese company. This would not be the first board supposedly Made in Japan that was really manufactured in Taiwan or China, but at least this “AT-BABY” uses almost exclusively Japanese components, whether it was actually assembled in Japan or not.
The BIOS can often aid in identifying an unknown board, but not in this case: Someone helpfully replaced the original BIOS with two EPROMs holding a 1990 AMI BIOS. That, on the one hand, is quite useful (the 1990 BIOS can handle user-defined hard disk types), but it also makes the board a little less original and a little more mysterious.
The chipset is the original Chips & Technologies CS8220 (that’s the one which coined the word “chipset”, or CHIPSet in C&T’s original usage), with all of the five individual chips made in Japan. The board does not use the C&T 82C206 integrated peripheral chip (the board design is likely just a bit too old for that), rather it uses discrete components exactly like a classic IBM PC/AT, but of Japanese origin: Two NEC D8237AC-5 DMA controllers, two NEC D8259AC-2 interrupt controllers, a NEC D71054C timer, a Hitachi HD146818P RTC, and even the memory chips are made by NEC. A sticker on the board says “MAXWARE Made in Japan” to reinforce the Japanese connection. The only major non-Japanese chips are an Intel 8742 keyboard controller and the Siemens SAB 80286-R CPU.
Apropos memory: Someone had harvested four 256 Kbit DIP memory chips from the board; there are two banks of eighteen chips each, and since the second bank was incomplete, only 512KB was usable (the board has labels the memory sockets as BANK0/1/2/3, but banks 0+1 and 2+3 are really only a single bank each as far as the chipset is concerned, since the onboard memory must be 16-bit; I will further refer only to banks 0 and 1, meaning the two 16-bit banks). Once I replaced the missing chips, the BIOS reported 640KB RAM… but what happened to the remaining 384KB?
This is where the unknown origin of the board was a problem. I could not find any information about the jumpers on the board. After some experimentation, I established that jumper block J29 controls the memory size, and I was able to select four different settings: 256KB (likely intended for use with two banks of 64 Kbit chips), 512KB (one bank of 256 Kbit chips), 640KB (one bank of 256 Kbit chips, one bank of 64 Kbit chips), and 1024KB (two banks of 256 Kbit chips).
There was just one remaining problem: With the 1024KB setting the board insisted on 512KB base + 512KB extended memory, not the arguably much more useful 640KB base + 384KB extended. So, how does one jumper the board to have 640KB base memory and not lose the remaining 384KB?
After consulting the CS8220 datasheet, I concluded that one doesn’t. The 82C202 chip has two input pins, SEL0 and SEL1, which allow for four combinations of memory layout, and those four combinations are exactly what I had already discovered through experimentation. To access the full 1MB RAM, the only option is to split it into 512KB base and 512KB extended.
That seems strange from a more modern perspective, but the CS8220 chipset was released in 1985 and was intended to be highly compatible with the IBM PC/AT. And the PC/AT simply did not support more than 512KB base memory on the system board—although a 16-bit 128KB expansion card could be used to increase the PC/AT base memory to 640KB. And that kind of board would very likely work the same in the Fujitech board.
The Chips & Technologies CS8220 is actually notable enough to have made IEEE Spectrum’s 2009 list of 25 Microchips That Shook the World, for enabling the widespread production of cheap AT clones. And it certainly did, as I established when going through the endless list of 286 boards listed on TH99.
The Fujitech board has a depressingly large amount of other jumpers (no DIP switches), and I was not able to determine their function except the above mentioned J29. Maybe someone actually knows what they are, or maybe I’ll someday try to figure what they do. So far after a few quick experiments, I only found out that one switch selects the ROM chip type (27256 vs. 27128). The remaining jumpers, when changed, simply prevent the board from working.
There’s also one extremely annoying oddity about the board: The power connector. The pinout is clearly standard AT, but the actual pins are not. They are round and the normal plastic shroud on the connector can’t be plugged into the board. Fortunately I was able to sufficiently mutilate a cheap ATX to AT adapter such that it can now be properly plugged into the board.
All in all, the Fujitech 286, whatever its actual provenance, is a classic AT design, probably difficult for software to distinguish from a true blue 8 MHz IBM PC/AT.