47 ms·

Author here for your IBM 1401 questions :-)

by kens 6y ago

addaon 6y ago
How 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 ago
  My 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 ago
  That'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 ago
What'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 ago
  I'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.
  - bsder 6y ago
    Is it possible this is DTL (Diode Transistor Logic) in IBM-speak?
    - kens 6y ago
      It's possible. IBM had several other types of diode-transistor logic including DDTL, SDTRL and CTDL. The emitter follower was more often used with ECL.
- kens 6y ago
  I 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 ago
Thanks for yet another great article! I was wondering about the inductor connected to the collector but you already answered in the footnote.
chmaynard 6y ago
Off 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 ago
  I 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 ago
    Seymour Cray expressed interest in germanium transistors in some speeches I have seen on Youtube. Mainly because of switching speed of germanium
bulleyashah 6y ago
Can 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 ago
  I'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 ago
  I 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 ago
  Since Vbe = const the transistor alone cannot amplify voltage. You need a resistor to convert the input voltage into current.
bogomipz 6y ago
The 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 ago
  Having 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 ago
    Wow 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 ago
      I'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 ago
More 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.

Author here for your IBM 1401 questions :-)

by kens 6y ago

Author here for your IBM 1401 questions :-)

How 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 ago
My 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 ago
That'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 ago

What'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 ago
I'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.
- bsder 6y ago
  Is it possible this is DTL (Diode Transistor Logic) in IBM-speak?
  - kens 6y ago
    It's possible. IBM had several other types of diode-transistor logic including DDTL, SDTRL and CTDL. The emitter follower was more often used with ECL.
kens 6y ago
I 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 ago

Thanks for yet another great article! I was wondering about the inductor connected to the collector but you already answered in the footnote.

chmaynard 6y ago

Off 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 ago
I 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 ago
  Seymour Cray expressed interest in germanium transistors in some speeches I have seen on Youtube. Mainly because of switching speed of germanium

bulleyashah 6y ago

Can 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 ago
I'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 ago
I 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 ago
Since Vbe = const the transistor alone cannot amplify voltage. You need a resistor to convert the input voltage into current.

bogomipz 6y ago

The 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 ago
Having 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 ago
  Wow 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 ago
    I'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 ago

More 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.