please S-100s started out with an Intel 8080, then Zilog Z80. That was pretty much the end of the 8-bit version, although there were several other variants (8085, NSC 800, Hitachi 64180, Signetics 2650, etc.). Hmm, I never recall seeing a 6502 or 6800 CPU board. Once the S-100 was standardized around the IEEE-696 specifications the good 16 bit systems started appearing. One of the earliest was the 8086 by Seattle Computer Labs (IIRC). Famous because it came with the ancestor of MS-DOS, which Microsoft later bought for their IBM PC deal. You might say all the PC software now in existence owes its existence to the S-100.... Anyway, there were quite a few 16-bit systems. Many 80286 variants, including a nice one by Macrotech, a dual Z80H/80286 CPU. There were several 68000s, TI 9900, National 32000, Zilog Z8000, and a variant on the Western Digital LSI-11 bit slice chipset called Alpha Micro. The AM ran its own multi-user operating system, very reminicent of RT-11 (there was a strong DEC influence there). Was the S-100 technically superior? Well, if you go by the IEEE-696 specifications then compared to either the XT or AT it was quite a bit better. Maximum memory was 16MB (24 bit address, 8 or 16 bit data path), 8 interrupt levels (open collector! which meant multiple boards could use the same IRQ), 16 DMA levels (still better than the 7 DMA levels on the current PC). Most 286 based systems ran up to 8Mhz reliably, some made it to 10 or 12 Mhz (compared to the original AT at 6Mhz). Even better, it was common practice to use static RAM memory on the better business systems. If that term doesn't sound familiar, cache memory on modern PCs is static RAM. The significance is that there were no wait states or lost cycles to refresh. Think of how fast your Pentium would run today if all 64MB of RAM was cache, not DRAM. S-100s were also very expandable. Motherboards usually had between 18 and 22 slots for full sized machines. You could put a lot of RAM, serial, and disk controllers in that many card slots. I built custom 286 based multi-user systems that supported 10 or more users running production business work. The response time compared quite favorably to contemporary low end DEC PDP-11s, and for a fraction of the cost. S-100s were also early adopters for much of the current crop of PC peripherals. Networking, using ARCnet at 2.5Mbps over coax. Digital Research supported network access to disk drives using CP/NET on top of MP/M II. No, it wasn't TCP/IP, but it still compares quite well to a basic Netware system. Disk drives, both the 5.25" floppy and the 5.25" hard drive showed up on S-100s before PCs. S-100s using MP/M II could support disk drives up to 512MB, long before MS fixed the 32MB barrier in the XT and AT. The S-100 did have some drawbacks, mostly from the weird control signals the CPU had to generate (anyone remember how difficult it was to simulate a PSYNC on a non-8080 processor?). It suffered terribly from early failures to standardize the bus. Many of the 8-bit systems had unsolvable compatibilty problems. (on the other hand, it did make for some extra pocket change for struggling college students who knew how to tune an S-100 to make everything work :) ) Another problem was the unregulated power supply. Unregulated +8 and +/-16VDC was run over the bus itself, right next to signal lines. Every board required it's own regulation, which could take 20% or more of the board space, as well as being a nightmare to keep cool. If you see early pictures of loaded IMSAIs, the cover was always off. This was a necessity, the heat was too much with the cover on. I had to use a 16" fan to keep mine running with 64KB of 2102 based static RAM (not 21L02s BTW, they cost more than the fan did). The single worst problem was the absolute lack of any hardware standardization beyond the 696 specs. There were no I/O addresses for anything. One manufacturer might use a WD 1791 floppy controller at port 7xH, another would use the NEC 765 floppy controller at address 9xH. There were no standardized BIOS ROMs either. Systems came with some basic boot ROM for one particular disk controller/serial interface, and that was it, everything else was supported by drivers in the machine specific version of the OS. A boot disk for an Altos wouldn't run on a North Star, not even close. For those who think it an evil that the world has standardized on the Wintel architecture for PCs, trust me, the other choice is far worse. Sure, but then if you wanted a good hardware oriented micro with lots of support from 3rd parties, in the mid 70s the S-100 was the only choice. You could get a board to do just about anything, tho you had to program it yourself. Nearly all boards came with schematics, if you didn't like the design or it wasn't quite compatible, you could cut traces and rewire to your own choosing. My own IMSAI is far from a standard out of the box model. society hardware _financially_ You don't like the profit motive? *gasp* That's, well, that's just plain un-american (understandable and excusable if you happen to be european tho). Jack "show me the money" Peacock