Welcome to the Living Computers blog! From oral histories and engineering restoration updates to behind-the-scenes looks and more, you’ll love the unique and personal stories we share with our community. Start exploring and get to know our team!

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Computer Maintenance Hell!
July 18, 2019
by Bruce S.
Back in October 2018, our PDP10-KI went down, and it didn’t want to come back up. I ran all the normal diagnostics, and they all worked, but the TOPS-10 would hang when I tried to boot it. That is the definition of Computer Maintenance Hell, Everything works, but the operating system won’t run!
Adventures in PDP10 Land
April 30, 2019
by Bruce S.
The PDP10-KI went down sometime in the fall, maybe October. This is the machine just to the right of the CDC6500 as you come in the second floor computer room. I noticed this fairly quickly and tried to reboot it, but it would hang when I tried, several times.
A Journey Into the Ether: Debugging Star Microcode
March 29, 2019
by Josh D.
Back in January I unleashed my latest emulation project Darkstar upon the world. At that time I knew it still had a few areas that needed more refinement, and a few areas that were very rough around the edges. The Star’s Ethernet controller fell into that latter category: No detailed documentation for the Ethernet controller has been unearthed, so my emulated version of it was based on a reading of the schematics and diagnostic microcode listings, along with a bit of guesswork.
Letting the cat out of the bag!
February 27, 2019
by Bruce S.
Back in September 2018, we got a new addition to the LCM+L computer collection, but we didn’t talk about it. This was something that we had been looking for for 10 years or more.
Bendix G-15 – Solder Degradation
January 22, 2019
by Keith P.
In the process of restoring the Bendix G-15, we have discovered a phenomena that degrades the electrical connections which provide bias and signal flow, rendering the computer non-functional.
Xerox ALTO – Interesting Issue
January 21, 2019
by Keith P.
We received our first ALTO in running condition and after evaluation and testing, put in on the exhibit floor available to the public. One afternoon about a year later, the machine suddenly froze and stopped functioning. It was taken off the floor and evaluated in one of our labs. When it became clear that power supply current was not flowing into random parts of the backplane, the focus shifted to the power supply rails. It was there we were confronted with this phenomena.
Introducing Darkstar: A Xerox Star Emulator
January 19, 2019
by Josh D.
In 1981, Xerox released the Xerox 8010 Information System (codenamed “Dandelion” during development) and commonly referred to as the Star. The Star took what Xerox learned from the research and experimentation done with the Alto at Xerox PARC and attempted to build a commercial product from it. 
Bendix G-15 Vacuum Tubes
January 18, 2019
by Keith P.
Early in the restoration and troubleshooting of the Bendix G-15 it was noted that tube filament failures occur with some regularity. It is not possible to observe working filaments on all the tube modules, as at least half the tubes have what is call a “getter coating” at the top of the tube, obscuring the filaments.
CDC Cooling update
January 18, 2019
by Bruce S.
In my last blog on the CDC, we were having a slow refrigerant leak in Bay 1, and we were waiting for parts. The new parts came, but they were wrong, then they came again, and they were wrong again. Eventually the right parts were delivered, so we took the CDC down yesterday morning to work on the cooling system.
DEC Computer Power Supply Module Retrofit
January 17, 2019
by Keith P.
In the process of troubleshooting our earliest machines, we had to replace large components called electrolytic capacitors. These are located in all the power supplies for any computer. We successfully replaced these devices and got the machines running. Recently though, we have started to see these devices fail once more. They have a finite life of a maximum of 14 years.
Life with a 51 year old CDC 6500
December 11, 2018
by Bruce S.
The CDC 6500 has led a rough life over the last 6 months or so: way back on the afternoon of July 2, 2018, I got an email from the CDC’s Power Control PLC telling me that it had to turn off the computer because the cooling water was too hot! A technician came out and found that the chiller was low on refrigerant. He brought it back up to the proper level, and went away. Next morning it was down again. ...
IBM at LCM+L
August 8, 2018
by Rich A.
As anyone familiar with LCM+L knows, the museum initially grew out of Paul Allen’s personal collection of vintage computers. Many of the larger systems in the collection reflected his own experiences with computers beginning in when he was still in high school. Among the systems he used then were System/360 ...
The DEC 340 Monitor, Ship It
July 2, 2018
by Keith H.
My last article explained that the DEC 340 Monitor pointed at and shot dots from an electron gun to light up spots on its screen. That was my magic chant, the method of how the DEC 340 drew its pictures as a collection of dots. Every picture a DEC 340 ever showed was made of dots flashed onto its radar tube ...
The DEC 340 Monitor, Magic Chant
June 23, 2018
by Keith H.
Previously I introduced my DEC 340 monitor restoration project. I promised then to describe how the DEC 340 monitor worked. I will, but that explanation won’t mean much without some context first. After the context the special magic that makes the DEC 340 different from other computer monitors will be revealed. High ...
The DEC 340 Monitor, The Introduction
June 7, 2018
by Keith H.
My big project this year is to get a DEC 340 monitor working. Here is a picture of one of them. The DEC 340 was a very early and rare computer monitor dating from the mid 60’s used of course, on DEC computers, their PDP series. Two cabinets of rack mounted electronics. The 340 is historic and was used ...
Testing old technology
May 2, 2018
by Bruce S.
I have 4500 modules in the CDC 6500, and it isn’t always easy to debug them in the machine, because convincing the machine to wiggle its lines so I can check each transistor on a particular module is difficult. In order to make this problem a little easier, I have built a cordwood module tester. It has taken a ...
What I learned Mapping Minecraft Worlds
April 27, 2018
by Jeff K.
Minecraft is getting a little stale for me now. I’ve done my exploring, and exploiting. Nothing left but… to look at the database! Each Minecraft world has its own folder in the save directory, with other subfolders and a lot of data files. I noticed that each map created in the world is a separate file, and that file is in GZip format ...
Detecting Nothing
April 26, 2018
by Jeff K.
The IBM360/30 gets stuck in a microcode loop. The documentation indicates that a branch should be taken if the Z-bus is zero, and the branch should be taken. The branch is not being taken. A previous annoyance was that the microcode would stop at address 0xB46. As the documentation indicates for that location, ...
New peripherals for old Computers
April 18, 2018
by Bruce S.
Five years ago, when we were getting done with restoring our PDP10-KI, we were running out of working disk drives to run it from. We were down to one set of replacement heads, two working drives, and we didn’t have a source for new ones. We found some folks that said they could rebuild the packs, but it turned out ...
That Pesky PS Module!
February 1, 2018
by Bruce S.
When we last left our hero, he had re-soldered all the Via rivets on one of the 510 “PS”, core memory sense amplifier modules in the CDC6500, and the machine was working. That lasted about a day, and the memory went away again. What was wrong this time? You guessed it, bit 56 in bank 36 was bad again. Third time ...
IBM360-30 Read Only Storage
January 29, 2018
by Jeff K.
The IBM360-30 uses Printed Card Capacitor storage for microcode. The cards were created by printing Silver ink on Mylar, or etched copper. 304 cards make up the microcode. I scanned them all. My procedure was to remove one card, clean it, scan it, and then replace it before removing the next card. My original ...
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