Fail Of The Week: Electromigration Nearly Killed This Xerox Alto

The Living Computers museum in Seattle has a Xerox Alto, the machine famous for being the first to sport a mouse-based windowing graphical user interface. They received it in working condition and put it in their exhibit, but were dismayed when a year later it ceased to operate. Some detective work revealed that the power supply was failing to reach parts of the machine, and further investigation revealed an unlikely culprit. Electromigration had degraded the contacts between the supply pins and the backplane traces.

If electromigration is new to you, don’t feel ashamed, it was a new one to us too. It’s “the transport of material caused by the gradual movement of the ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms“, got it? Okay, that’s just a long way to say that passing a sufficiently high current through a conductor for a long time can physically move the metal of that conductor.

This one just doesn’t pop up very often. But in the case of the Alto, an under-specified power distribution system caused a lot of current to flow through too few solder joints. Those joints were left without enough metal to make a decent connection, so they failed.

The fix came with a set of sturdy busbars freshly soldered to the pins, but the interest in this piece comes more from the unusual phenomenon that caused it. That soldered joints can seemingly flow away defies belief. It’s still something most of us will never encounter, but like tales of ball lightning it’s one for the “Fancy that!” collection.

We’ve covered the Alto before, most notably [Ken Shirriff]’s work in restoring the Computer History Museum’s example.

Diablo Drive Appears To Be Cursed

[CuriousMarc] didn’t think it would be a big deal when a former Xerox employee sent him an Alto Diablo drive for service. Turns out the drive was cursed — it would destroy everything it touched including a set of heads and an alignment cartridge. [Marc] and a partner spent two months trying to get the drive operable and the video of their process is pretty interesting.

We were interested in the troubleshooting, but we were really envious of their lab, full of HP workstations, an IBM mainframe, and even a Selectric. We kept having to rewind the video because we had tuned out while we were staring at some of the equipment in the background.

The guys got a lot of practice aligning the heads on the drive. Because the crashed head was bent, it actually dug into the alignment cartridge so on subsequent attempts they had to manually load the disk past the damage. They learned to leave the disk a little out of alignment because tightening the assembly will move it a little bit. If you were already aligned, the heads would be off after you did the tightening.

They used a custom FPGA-based tester that [Carl] developed after reverse engineering the disk format. It is amazing to watch the big drive in action and realize that a standard cartridge for this machine was 2.5 megabytes. There was another controller and disk system called the Trident that would get you a whopping 80 megabytes, but we don’t think this is one of those.

Did they succeed in exorcising whatever demons lived in the drive? Watch the video and find out. Even if you never have to fix a Diablo drive yourself, you’ll be entertained. Especially when they work out how to do a current adjustment on the drive by simulating the circuit in Spice.

We’ve seen a lot about the Alto which is surprising considering how few of them were built. We’ve seen a restoration and even an odd use for a light bulb related to the Alto’s CRT.

Continue reading “Diablo Drive Appears To Be Cursed”

World’s Worst Bitcoin Mining Rig

Even if we don’t quite understand what’s happening in a Bitcoin mine, we all pretty much know what’s needed to set one up. Racks of GPUs and specialized software will eventually find a few of these vanishingly rare virtual treasures, but if you have enough time, even a Xerox Alto from 1973 can be turned into a Bitcoin mine. As for how much time it’ll take [Ken Shirriff]’s rig to find a Bitcoin, let’s just say that his Alto would need to survive the heat death of the universe. About 5000 times. And it would take the electricity generated by a small country to do it.

Even though it’s not exactly a profit center, it gives [Ken] a chance to show off his lovingly restored Alto. The Xerox machine is the granddaddy of all modern PCs, having introduced almost every aspect of the GUI world we live in. But with a processor built from discrete TTL chips and an instruction set that doesn’t even have logical OR or XOR functions, the machine isn’t exactly optimized for SHA-256 hashing. The fact that [Ken] was able to implement a mining algorithm at all is impressive, and his explanation of how Bitcoin mining is done is quite clear and a great primer for cryptocurrency newbies.

[Ken] seems to enjoy sending old computer hardware to the Bitcoin mines — he made an old IBM mainframe perform the trick a while back. But if you don’t have a room-size computer around, perhaps reading up on alternate uses for the block chain would be a good idea.

[via Dangerous Prototypes]

Restoring The Groundbreaking Xerox Alto

The Xerox Alto was a minicomputer that had a lot of firsts to its name: first GUI, first Ethernet connection, and first computer to use a laser printer. This is the computer that inspired Steve Jobs to build the Lisa. And this was built all back in 1973! So when [Ken Shirriff] and a team of other old-computer aficionados got their hands on one, you know they’d get to work.

[Ken]’s blog describes the start of what’s sure to be a long journey. It mostly describes the Alto system and locates its place in computer history, but there are some interesting sidelines as well — like how [Alan Kay] also basically outlined all of the functionality of the modern laptop / tablet along the way to the Alto; it was supposed to be an interim Dynabook.

Work on this grandfather-of-modern-computers is just getting started, and [Ken] and crew are dusting off the power supplies and cataloguing memory boards. You can be sure that we’ll follow along with this restoration project, and keep you informed.