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Germanium transistors: logic circuits in the IBM 1401 computer
- kens 6y agoAuthor here for your IBM 1401 questions :-)
- addaon 6y agoHow similar or different are the performance characteristics of the NPN-based and PNP-based gates? Assuming there's a meaningful difference, are there signs in the design anywhere where this was considered? Thinking of cases where complex logic is pushed to the NPN stages and the PNP stage is used for just an inverter, or similar patterns.
- Ccecil 6y agoMy memory...which is very hazy and limited on this topic...is that the Germanium based transistors have a VBE of .3v instead of silicon's VBE of .7v So in things like amplifiers it gives you less zero point crossover distortion. In digital I believe it lends to a faster switch time but I could be very wrong on this part. Germanium is much more rare so the cost is naturally higher...from what I know.
- kens 6y agoThat's an interesting question. Looking at the documentation the NPN card (CHWW) and the PNP card (CGWW) have different switching characteristics (NPN is faster on and slower off). But I haven't noticed any difference in usage patterns.
- yholio 6y agoWhat's DEFL - Diode Emitter Follower Logic, suppose it's IBM's name for ECL? Do we have examples of these circuits being used in critical circuits in mainframes of the 60s? I can't imagine a logic circuit of that era that was technically capable of being clocked at 100Mhz, 30 years before these frequencies became the norm.
- kens 6y agoI've looked, but I can't find anything more about DEFL. (The table says it was used in certain serial numbers of the core memory for the Stretch computer, so it seems rather obscure.) Based on the speed, it's plausible that it is a type of ECL, but I don't know where the diodes would fit in. IBM had other names such as current-steering logic for ECL. Keep in mind that the 10ns speed doesn't mean you can run at 100 Mhz, since there are likely to be multiple levels of logic, as well as other delays. But it's still pretty fast.
- kens 6y agoI found an IBM patent for high-speed logic using diodes and an emitter-follower. I don't know if this is "Diode Emitter Follower Logic" but it kind of matches the name. https://patents.google.com/patent/US3050641A/ https://patents.google.com/patent/US3050641A/
- jecel 6y agoThanks for yet another great article! I was wondering about the inductor connected to the collector but you already answered in the footnote.
- chmaynard 6y agoOff topic: I understand that William Shockley was interested in exploring germanium semiconductors, which may have been a contributing factor in the exodus of eight of his senior scientists and engineers to form Fairchild Semiconductor. Could you comment?
- kens 6y agoI haven't heard anything about Shockley wanting to explore germanium. My understanding is the "Traitorous Eight" left both because of personality conflicts with Shockley and because he was focusing too much on his 4-layer diode instead of transistors.
- UserForANow 6y agoSeymour Cray expressed interest in germanium transistors in some speeches I have seen on Youtube. Mainly because of switching speed of germanium
- bulleyashah 6y agoCan I ask a really basic question? I understand that transistors amplify current but how do they amplify voltage (like in CMOS)? Isn't voltage going to amplify current also? I never understood this.
- kens 6y agoI'm not sure I can answer that without confusing things more, but I'll see what I can do. In an MOS transistor, the gate is insulated, so there is no base current, just voltage. This voltage controls the transistor. In a bipolar (NPN or PNP) transistor, the current through the base causes a larger current through the collector, amplifying by the beta factor. So the transistor is amplifying current. But the current depends on the voltage between the base and emitter, so from that perspective the voltage controls the transistor too. Whether you're amplifying current or voltage depends on the circuit, so I can't give more than a handwaving answer.
- dfox 6y agoI will also try. In field effect transistor (in which the actual physics involved are at least for me simpler to grasp) the gate is isolated from everything else and voltage at the base directly changes the geometry of the conductive channel between the S and D pins. In effect the gate voltage directly influences the resistance of the component. MOS is an name for particular practical realization of this mental model. In bipolar junction transistor (ie. PNP/NPN) there are two diodes that are positioned just so that conduction of one of them influences the other in such a way that when one is positively biased the other will conduct even when reverse biased. For the typical BJT these two diodes have significantly different construction and thus there is difference between emittor and collector, but the effect works both ways (and in fact many circuits will somewhat work even with the 2N3904 connected the wrong way around). The effect is also caused by change of properties of doped semiconductor material in response to electric field gradient but (at least for me) there is no directly applicable model involving discrete lumped components changing their parameters in response to external stimuli that matches the underlying physical principle.
- Koshkin 6y agoSince Vbe = const the transistor alone cannot amplify voltage. You need a resistor to convert the input voltage into current.
- bogomipz 6y agoThe photo of the card drawer open is really spectacular. I am curious how they identified faults with that number of individual cards. Any insights into that?
- kens 6y agoHaving tracked down a few problems in the IBM 1401, it's basically a matter of figuring out what the overall problem is, and then looking for a signal that indicates the problem. Then you work backwards through the circuitry, probing signals with an oscilloscope until you find something that might be the root of the problem. Then you can swap the potentially-bad card and hopefully it fixes the issue. Of course, some times this is easy, and some times it is hard. Once you find the bad card, the restoration team likes to fix the bad card rather than just replace it. This can have its own challenges. I spent a long time trying to fix a card from the printer that ended up having a cracked trace that was intermittently bad. All the signals looked good, yet the card didn't work. For a detailed look at a problem, I wrote a blog post about a core memory problem that turned out to be an inductor that failed open. After fixing that, the computer wouldn't power on. We replaced some weak transistors in the power supply, but that didn't help. Finally we found an undocumented fuse that had blown, probably from one of the boards we swapped. Replacing that got everything running again. http://www.righto.com/2017/12/repairing-1960s-mainframe-fixing-ibm.html http://www.righto.com/2017/12/repairing-1960s-mainframe-fixi...
- bogomipz 6y agoWow this link is fascinating! How fun that you got to be a part of that. I'm trying to imagine an IBM field tech back in the day being called to a customer site and having to go through similar with a customer who was renting one of these for exorbitant sums. It must have been stressful. I'm sure there was some sort of SLA.
- kens 6y agoI've talked to old-time IBM service engineers and IBM would do just about anything to keep a customer's computer running. An engineer could call his boss and say that a customer needed a very expensive replacement core memory, and IBM would send someone on the next flight to deliver it. If the customer was in the middle of nowhere, someone would drive out with a part and the engineer would drive to meet them halfway. There's a reason people say that nobody ever got fired for buying IBM.
- tal8d 6y agoMore an IBM archeology question: aside from the scattered projects to catalog specific product lines, are you aware of a more general effort? I've been pulling together a lot of their research papers and documentation related to the POWER architecture for a while, and I've noticed some pretty big missing pieces. For example: in order to best preserve the pdfs, while increasing their usefulness and reducing their maintenance burden (disk space), I set out to convert them to PDF/A. That means embedded fonts, which is fine - I'd ideally digitize as much of the text as possible (instead of throwing a hidden OCR layer on and calling it a day), but... the font is nowhere to be found. IBM had an extremely popular font, Press Roman, that is very common in journals and books published from the 60s to the late 80s, and as far as I can tell - it may now exist only in whatever remains of two printer font cartridge SKUs. I won't even get started on the problem regarding their plotting software. It reminds me of how NASA simply lost so much of the original media, and what he have today is either purely accidental or the result of a considerable amount of work done by volunteer restoration groups. We really need to get a grip on this problem now, and it would be nice if IBM would actually help out with that - instead of leaving it to volunteers.
- kitotik 6y agoNeat! NOS germanium transistors are still highly sought after(and therefore expensive) for music gear such as guitar distortion pedals and pre-amps. They impart a lovely ‘gooey’ quality that modern transistors just can’t do.
- gkhartman 6y agoYep, I have a diy fuzz effect pedal around here somewhere that uses a matched pair of germanium transistors. An older electrical engineer gave me a box of them after I explained how sought after they were. He couldn't get his head around the idea that I would want to use them in a new project when new silicon transistors would be superior for many reasons.
- kens 6y agoIt seems like audio applications like to use old parts: how do germanium transistors compare with tubes?
- Ccecil 6y agoTubes are better since they have amplify with less "zero point crossover distortion". Silicon has .7v and Germanium has .3v Vbe so that is why people seek them. My understanding though is that it is something you can tune by adding biasing diodes but requires matching. I am not an expert...just something I remembered from school :) https://en.wikipedia.org/wiki/Crossover_distortion https://en.wikipedia.org/wiki/Crossover_distortion Edit: added Vbe
- squarefoot 6y agoCrossover distortion is completely inaudible if the amplifier is correctly biased as it amounts to a fraction of a fraction percent of the output power, like attempting to listen to a distorted 100 mW pocket radio put on top of a perfectly linear 500W amplifier set at maximum output. The difference between germanium and silicon transistors lays in the former having much narrower bandwidth, so that it naturally and more gracefully limits higher audio frequencies, and some the artifacts of distortion become less audible making the sound more warm. Tubes are better than both in this context because they saturate in a really graceful way and produce mostly even harmonics which give tube guitar amps their unique different sound; this is something hardly reproducible in solid state, unless DSPs are involved. I wouldn't however use tubes for clean HiFi amplifiers as more modern technologies such as Class D today made possible building incredibly good amplifiers at a fraction of the cost, space and energy requirements. They can also be used for guitars, but as Class D stages distortion sounds like pure junk, everything has to be redesigned so that the final stages are kept clean and distortion happens before entering them.
- myself248 6y agoNot specifically about the 1401, but where do you find the time to produce this volume of high-quality content that obviously takes a ton of work and research?
- mathiasgredal 6y agoFrom what i have read, with my limited understanding of chipmaking, it seems that UO2(Uranium dioxide) makes a great heat and radiation resistant semiconductor with better properties than silicon or germanium[1]. So how come we arent using that or exploring other materials for pushing the limits of computational power? [1]: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.522.5718&rep=rep1&type=pdf https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.52...
- userbinator 6y agoThe mere mention of uranium is going to make the paranoid scared, and nuclear regulatory agencies raise much concern. Even "depleted" uranium is somewhat radioactive, and it's a toxic heavy metal.
- ClumsyPilot 6y agoA modern pc is toxic, it's not like you could survive stuffing an iPad in a blender and eating it. Thats why e-waste is causing so many problems.
- a1369209993 6y ago> it's not like you could survive stuffing an iPad in a blender and eating it To be fair, I think the sharp chunks of metal and plastic would kill you before the heavy-metal poisoning could.
- kens 6y agoI doubt an iPad would kill you. One guy ate 7 TV sets, a computer, bicycles, and an entire Cessna 150 aircraft. https://en.wikipedia.org/wiki/Michel_Lotito https://en.wikipedia.org/wiki/Michel_Lotito
- totalZero 6y agoThe Frenchman ate an airplane and died of natural causes at the age of 57. Now there's a sentence that I never thought I'd write.
- tal8d 6y agoFunny, I was just over on ibm1130.org the other day - so the ALD diagram jumped right out. http://media.ibm1130.org/1132_Printer_ALD_Jun67.pdf http://media.ibm1130.org/1132_Printer_ALD_Jun67.pdf