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D > DIGITAL EQUIPMENT CORPORATION > RAINBOW 100


Digital Equipment Corporation
RAINBOW 100

Untitled Document

Chris Ryan reports:
There were two versions : the model 100 & The model 100+. The 100 had 64 KB soldered RAM and the 100+ had 128KB with a socket expansion for an other option board.

The system was triple boot (in bios, and could be set for automatic default boot preference on 100+) and booted in either CP/M, DOS, or VT100 mode.
When booted in DOS, the Z-80 acted as an I/O co-processor for the 8088 side, and visa-versa for CP/M mode.
The 8088 could also be upgraded with an NEC V-20 chip, but it involved either doing an E-PROM hack (published) or manually selecting the boot mode each time. (It was due to the V-20 being so much faster, and the post used a step/increment timing sequence, the system would respond faster than the number of clock cycles it was told to wait until looking for a response.)

There was also an after-market 80286 upgrade available, and an after-market HD controller upgrade that allowed 2 HD's instead of the standard 1 HD. The HD was limited to 2 32MB partitions for DOS, and I forget how many 8Mb CP/M partitions (simultaneously).

The system used an NEC-based UART, not Intel, so standard DOS based communications programs wouldn't work on it. However, when using FOSSIL or other proper comm layers, the system was capable of handling 9600-14400 without any dropout. Tres-cool. Many people were able to run FIDO BBS systems on it, using US Robotics HST modems at 9600 baud.

There were Rainbow-specific versions of Lotus, Wordperfect, Wordstar along with software from DEC Timings done with the system that the PC couldn't beat on most functions until the PC-AT (10Mhz model at that).

Another computer brought out by DEC was the VAX-Station, which used an 80286 processor. Full PC compatibility along with VAX compatibility (the ALPHA systems greatly surpassed it, maybe that's why this system never was promoted).

Bill LaGrue reports:
The floppy drive was a pretty unusual piece of equipment. As mentioned the disks were formatted in a proprietry format, but they were only single sided. The disk drive actaully contains 2 drives, but there is only one motor inside that drives the center spindle by some belt arrangement from memory. The result is, that besides the disks being single sided, so they rotated in the correct direction the top disk faced "up" and the bottom drive faced "down". There was a big orange stripe on each of the drives, and the genuine DEC floppy disks also had a big orange stripe on them, so to make sure you had inserted the disks the right way up you had to match up
the stripe on the drive and the disk.

On my particular machine, I had Lotus 1-2-3, Wordstar, and Turbo Pascal, besides some other generic CP/M-86 games (Nethack!!!! and Moria!!!!) and a
couple of generic MS-DOS games (Nethack!! and Rogue!!). The VT-100 terminal emulator came in handy, I could dial up the university manually, the press
the button on the modem and work from home.

Along the back of the machine was a row of 7 or 8 LED's - they were the machines self-test. As the machine powered up you could watch the LED's cycle through. In the manual there was a big chart of all the LED combinations, so if something went wrong it was fairly easy to identify what it was. On one occasion, the machine wouldnt boot, and the LED's indicated there was a prolem with the Z80, so I went down to the local electronics shop, bought a replacement, put it in the socket and the problem was fixed.

The keyboard used to plug into the back of the monitor, which in turn plugged into the box, so it was possible to have the keyboard/monitor quite a distance away from the main box. There were a number of expansion cards available - a memory expansion, a graphics card expansion, and a hard drive controller. Each card had its own dedicated socket on the mainboard. The cards actually plugged in flat over the top of the main board, rather than standing up like modern PC's. As far
as I am aware, the graphics modes were not available unless you had bought the extra graphics card, which I didnt have. I did however have an external 10Gb hard drive :)

Sound was limited to a beep. I'm fairly certain that it had no parallel port, just 2 serial. I remember that because I was very limited in what printers I could use.

Denis Frocier adds:
There was another "external comm" adapter available that that brought out an RS-432 port. These were rare but I have one. (I have two 100+'s plus full documentation and accessories (like the motorized workstation).)

The floppy drive *could* be made to read (and write?) the IBM PC format with an add-on program. Software-wise that wasn't a big problem. The issue was that the DEC format was high density (as dense as the 1.44MB PC format) and the track widths were correspondingly narrower. PCs with low-density drives would often as not get read errors on the DEC disks, but the high density drives would read (and write?) them just fine.

The serial printer port wasn't such a limitation as might be supposed now. Most printers at the time had both serial and parallel. Given the print speeds there just wasn't any need for a really fast port, and with two serials you could connect two modems if you wanted.

Tom Creviston's memories:
I sold these machines out of a small computer store here in Indianapolis, Indiana. As I recall, there was an extensive user base that communicated through BBS (bulletin board systems).
Someone supplied a format program (free) that allowed you to sysgen new disks so you didn't have to buy them from DEC and someone else figured out that if you cut a square notch opposite the write protect notch you could put your disks in upside-down and write on the other side, doubling your storage (as far as I am aware, the first instance of DSDD [I could be wrong about this]). Anyway, a great machine that made effective use of multi-processors in it's day.

 





 
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