DEC desktops

[DEC desktop no cover] I acquired three DEC desktop computers during spring-summer of 2013. This page is a description of my initial work to test and operate them. I have many DEC computers which are listed on this linked Web page. I have in particular, a PDP-8/f which is largely operating, thanks to work done on that 8/f as of April 2013.

Last updated July 7 2013. Edited by Herb Johnson, (c) Herb Johnson.

common features

[DEC Rainbow 100] Here's a nice enough view of the case, of the Rainbow 100. The DecMate series and the Professional series look the same. The floppy drive is on the far right of the case: DEC used their own pair of stacked 5.25-inch drives.

[DEC desktop no cover] Here's one of the desktop computers with the covers off. The black box in the middle of the desktop is the 5-inch wide hard drive. Here's a partial view of the DECmate II hard drive. Note the head rotating mechanism is outside the hard drive case. The hard drive light is on and this drive is operating. To the right of that, is a stacked pair of DEC floppy drives. to the left, is the power supply and a power switch. This configuration is common to these three DEC desktops; the power supply may be at the rear rather than the side.

To the right of the desktop is a video monitor and keyboard interface, the DEC VR201. The keyboard is the DEC TK201. There's a 15-pin DB-15 connector between the monitor and desktop; the keyboard RJ-11 plugs into the monitor. The DB-15 supplies video, power, and accepts a 4800 baud serial link to and from the keyboard. Here's a text document describing the DB-15 connector. I wired up a set of cables to operate these DEC desktops.

[DEC Rainbow 100] The main board or motherboard of these desktops, pulls out from the back. There may be vertical cards to be removed first, and some cables.

DECMate II PDP-8 desktop

The DECMate II is a PDP-8 compatible computer using the Intersil 6100 series microprocessor. The DECMate II was sold as an office text editing and data system.

[DECmate II] This is a photo of the "master menu" not long after booting up the resident OS, version 1.2.

[DECmate II] Labels on the back show this is a model PC278-A1. PC278 was another designation for this DECmate model. The tag H7842B is likely the power supply part number.

[DECmate II] On first boot, this message appears: ROM level 19M or 19N, data level 0412.

[DECmate II]

[DECmate II] A number of menus are available from the OS. Eventually I found a "drive test" feature and ran it. Here's one of the resulting messages: device 0, 590 blocks checked, 0 errors. the other message says, for device WPSSYS, no documents, 316 blocks free.

DEC Professional 350

[DEC Pro 350] The DEC Professional 350 is a PDP-11 compatible computer. In this boot-up screen image, the error message says "memory board option not functioning...error byte 007, status byte 000". there's two RAM boards with this particular system. In the lower right, there's two numbers: 060007 and 000034.

[DEC Pro 350] The screen after boot, shows that P/OS version 3.0 loaded from the hard drive. I did not have a login name and password, so I could not log in and operate the system further.

I did my initial work on this Pro 350, at the MARCH fix-it even of May 2013. This photo shows the 350 motherboard with vertical cards in place. At the time, the hard drive did not "seek".

DEC Rainbow 100

The DEC Rainbow 100 is an MS-DOS compatible desktop computer. That is, it runs MS-DOS and has an Intel 8088 processor. It was produced in the days before "100% IBM-PC compatible" was established as "the standard" Intel/Microsoft PC.

[DEC Rainbow 100] [DEC Rainbow 100] Here's a nice enough view of the case on the left. On the right, the motherboard is partically pulled out. It includes some daughtered boards atop it. This unit happened to be very dusty.

[DEC Rainbow 100] This particular desktop computer did not have a hard drive in it. So no OS came up: this screen is the generic bootup screen. Apparently the ROM set is 04.03.11A.

Contact information for Herb Johnson:
Herb Johnson
New Jersey, USA

This page and edited content is copyright Herb Johnson (c) 2013. Contact Herb at, an email address is available on that page..