Sorry all, I'm delayed (on digest and backlogged anyway). But: RB100B == RB100+ except that the + included the HD and HD controller card. RB100A has 64kB on-board, can accept 3 256kB banks of RAM (with the right adaptor card and memory card) for a max. of 832kB, or 3 64kB banks with just a memory card for 192 kB total. RB100B/+ has 128kB on-board, doesn't need an adaptor to go to 896 kB with the memory card. In addition to the boot-from-Winchester option being present in the later models, there are some other differences in the ROM, enough that the dvorak keyboard remapper I have won't work on my 100A, though it's reported to work on the 100B or 100+. (Project #1 for when I get sufficient spare time.) B and + support the "Compose Character" key on the LK-201 (?) to generate overstrike characters. Here's how the Graphics option works (colors or monochrome intensities displayed before the slash, all available after the slash): +---------------+---------------+ |Med. Resolution|High Resolution| +----------+-------+-------+-------+-------+-------+ | Config. | Model | Color | Mono. | Color | Mono. | +----------+-------+-------+-------+-------+-------+ |Monochrome| 100-A | N/A | 4/4 | N/A | 4/4 | | Monitor +-------+-------+-------+-------+-------+ | Only | 100-B | N/A | 16/16 | N/A | 4/16 | +----------+-------+-------+-------+-------+-------+ | Color | 100-A |16/1024| N/A | 4/1024| N/A | | Monitor +-------+-------+-------+-------+-------+ | Only | 100-B |16/4096| N/A | 4/4096| N/A | +----------+-------+-------+-------+-------+-------+ | Dual | 100-A |16/4096| 4/4 | 4/4096| 4/4 | | +-------+-------+-------+-------+-------+ | Monitors | 100-B |16/4096| 16/16 | 4/4096| 4/16 | +----------+-------+-------+-------+-------+-------+ Tony Duell has published on this list a good description of how to make a cable to allow dual (VR-201 and e.g. VR-241) monitors. It should be in the archives, but I have a copy and can email if desired. My 100A has a DEC 8087 coprocessor board which also serves as a memory adaptor, and is stuffed up to 832k. It has an upgraded (100B or 100+) power supply and a HD controller with an ST-225 as the hard disk. BTW, I have not seen a 100A power supply, but they are referred to in multiple reasonably believable places. Rainbow MS-DOS was different from PC-DOS. The last version, MS-DOS 3.11b, was a third-party (Suitable Solutions, who also did the ClickClock and TurBow) effort that also supported "Code Blue" (from the same vendor), which I guess was an attempt to patch the incompatibilities. It was supposed to have done pretty well but not perfectly. - Mark