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A "Outsider's" view of an IBM 1401A sample from "An Engineer’s Memoir of Teletype Corporation "
By Jim Haynes
from Southwest Museum of Engineering, Communications and Computation.
with comments about IBM 7090 and the IBM 1401 as off-line I/O, and circuits
Comments by "Insiders" ;-)
It was during this time that I first got up close to a digital computer.20 Edwards had an IBM 704, a vacuum tube machine which by then was fairly obsolete. The computer was kept busy with scheduled work during the day and evening. On graveyard shift engineers with problems to solve were allowed to use it hands-on.
One of my friends from the rocket site was an aeronautical engineer who was doing some work in FORTRAN, so I asked him if I could tag along the next time he was going to do a computer session. He told me to dress warmly, because they kept the temperature in the computer room around 60 degrees to improve machine reliability. We got to the machine room just before midnight and met several other engineers who had signed up to use the machine that night. The idea was that one
20 I had taken the one computer course offered in Electrical Engineering at the U of A; but we didn’t have a computer there at the time. During my last semester there the Agriculture school acquired a Bendix G-15 computer, which was to be used to breed bulls. I never got to see it.
would run his program, and while he was figuring out how to correct the inevitable errors another would be using the machine.
The lone computer operator turned the machine over to us and retired to a warm office. The process was to read some cards that started the FORTRAN compiler, then to read a deck of cards containing the program. A horrid old 100 lines-per-minute printer would produce a listing; and if the program wasn’t too bad the machine would eventually punch out a deck of cards containing the executable program. Then you put those cards in the reader and started the machine again. All this was accompanied by much spinning of reels of tape.
One of the engineers was quite knowledgeable about the computer. He would sit at the console and now and then stop the machine and examine something in the big panel of lights; or maybe he would manipulate the switches to alter the value of a variable or part of the program. The rest had to make do with what the printouts told them.
After a few hours of this, during which I closely examined a lot of the hardware to see how it was built, one of the engineers concluded that the machine was malfunctioning. He called in the operator, who ran a test program that confirmed something was wrong. The operator said he would notify the IBM field engineer when he came in in the morning, and we all went home to bed. “Some nights you get your work done, some you don’t,” was what they told me.
A little later the 704 was replaced by a more modern IBM 7090 transistorized computer. I mentioned earlier that in those days transistors were fast enough for use in Teletype equipment but were too slow for computers. In the 7090 IBM had got around the problem by using some special kind of “drift” transistors and emitter-coupled logic. The transistors were fast (well, 60 MHz was fast in those days) only if the collector-to-base voltage was about 6 volts. To get around the voltage offset from input to output there were circuits with NPN transistors and one set of logic voltage levels, and others with PNP transistors and a different set of levels.
Logic designers had to alternate stages of circuits of the two kinds. It took quite some time for IBM to get the 7090 all installed and working, perhaps a couple of months, so I got a good look at the innards of the machine before it was closed up and the machine room was closed to visitors. It was built out of the IBM SMS circuit cards, slightly larger than those used by Teletype and having thinner lines and more edge connector fingers.
These cards were assembled by automatic machinery. The backpanels were all wire-wrapped automatically by Gardner-Denver machines. I later learned of something really weird about the 7090. It used an eight-phase clock. A cable carrying the clock signals between two cabinets had as much time delay as one phase of the clock. The wire labelled “phase 1” at the sending end of the cable was labelled “phase 2” at the other end
because by the time the phase 1 pulse got through the cable the time was phase 2 at the sending end. This could have driven someone batty, a cable with different names at the ends of a piece of wire.
For some reason the 7090 systems employed the same lousy card machines and line printers that were supplied with the 704. These were never used in normal operation. Instead every 7090 site had at least one 1401, a small computer which was used as a card-to-tape and tape-to-printer converter.
Card decks were fed into the 1401 and written to tape; then the tape was manually moved to the 7090. A small monitor program in the 7090 read the tape and ran the jobs one after another. Output went to another tape drive. When the output tape filled up it would be carried to the 1401 for printing. The 1401 had really nice peripherals, especially the 1403 printer. This ran at 600 lines per minute and used a print chain rather than a drum. It was very impressive to watch; and it made an impressive amount of noise.
It was really a new generation of printing technology. In drum printers the same character is present at all print hammer positions at a given time. In chain printers there is a different character at each hammer position. Hence it was necessary to scan all the characters in the chain and compare with all the characters to be printed before each hammer strike time.
For the end users the big improvements were in print quality and in the possibility of having changeable print chains with different fonts. With drum printers any timing errors in the print hammers cause characters to be printed above and below the print line, which is highly noticeable. With chain printers the timing errors affect the horizontal spacing between characters and are much less noticeable. Chain printer technology was later adopted by General Electric for the Terminet terminals and by Teletype for the Model 40 21.
The 1401 was a fairly slow small computer, built with complementary saturated transistor logic. Texas Instruments had developed the 2N130x family of transistors, pretty slow by later standards but faster than what had been normal22. The circuits used NPN and PNP transistors in alternating logic stages, as in the 7090, but for a different reason.
The transistors were operated in saturated mode, so the two different voltage levels were just a matter of providing turnoff bias to the transistor bases. The NPN stages might have emitters at ground and collector pullup resistors going to +12 volts. The PNP stages then would have emitters at +6 volts and collector resistors going to -6 volts. This seems to save some parts
21 Brodrueck patent No. 3,845,710, Nov. 5, 1974
22 In fact, IBM had developed automatic machinery for making the transistors. Then IBM management decided they did not want to tie up capital in component manufacturing and sold the whole works to T.I.
count because the collector pullup resistor of one stage is also the base pulldown resistor for the following stage. Each transistor stage was a voltage inverter but was not considered to invert the signal logically. A logic inverter was an emitter follower, so it didn’t invert voltage.
For their transistor machines IBM had developed an elaborate design automation software system. Engineers drew logic diagrams on special sheets, which were then keypunched by clerks. The software worked out the wiring of the machine. It had a data base of all the different circuit cards so it could check for things like overloaded signals and incompatible connections.
When all the errors were got out it would generate a card deck of instructions for a Gardner-Denver wiring machine and print logic diagrams on a line printer using a special font that included vertical and horizontal lines and corners of boxes. Aside from the saving in drafting labor this practically guaranteed that the logic diagram agreed with the way the machine was actually wired. Logic signals could have fairly long names, enough to make the logic diagrams largely self-explanatory and reduce the amount of written explanation of how the logic worked. It was quite an impressive accomplishment, particularly in an era when a large computer had 4096 36-bit words of memory.
My engineer friends complained about the IBM 7090 operation; they were no longer allowed to come in late at night and have hands-on access to the machine. They had to leave a card deck in the evening and pick up the results the next morning. The slightest mistake in the cards meant waiting another day for results.
One group of engineers on the base had their own IBM 1620 computer. This was a small slow machine. On this particular one the only printer was an IBM electric typewriter, so they had to learn to write programs that solved their problems without producing much output. Edwards AFB at that time also had a large punched card accounting operation using electromechanical card machinery.
Comments by "Insiders" ;-)
- From Robert Garner, - December 28, 2019
- From Michael Albaugh, - Dec 31, 2019 11:22 pm
- From J. H. McCarthy, - Jan 01, 2020 11:28 am
- From Rick Dill, - Jan 01, 2020 12:26 pm
From Robert Garner, - December 28, 2019
CCing some "Insiders", John Pokoski, Jud McCarthy, and Rick Dill
Here, the author didn’t know or relate that the 1401’s Ge transistors had actually been developed by IBM (not TI) and were still labeled with IBM’s nomenclature (033, etc), not 2N130x :
"Texas Instruments had developed the 2N130x family of transistors, pretty slow by later standards but faster than what had been normal22”
"22 In fact, IBM had developed automatic machinery for making the transistors. Then IBM management decided they did not want to tie up capital in component manufacturing and sold the whole works to T.I."
I’ve wondered whether IBM's schematic entry and ALD creation software performed any circuit rule checking (or perhaps even static timing analysis). This sentence seems to confirm some degree of rule checking: "
"For their transistor machines IBM had developed an elaborate design automation software system. Engineers drew logic diagrams on special sheets, which were then keypunched by clerks. The software worked out the wiring of the machine. It had a data base of all the different circuit cards so it could check for things like overloaded signals and incompatible connections."
I’m not sure what the author meant here by: “each stage was a voltage inverter but not considered to invert the signal logically” and “A logic inverter was an emitter follower, so it didn’t invert voltage":
“The transistors were operated in saturated mode, so the two different voltage levels were just a matter of providing turnoff bias to the transistor bases. The NPN stages might have emitters at ground and collector pullup resistors going to +12 volts. The PNP stages then would have emitters at +6 volts and collector resistors going to -6 volts. This seems to save some parts count because the collector pullup resistor of one stage is also the base pulldown resistor for the following stage. Each transistor stage was a voltage inverter but was not considered to invert the signal logically. A logic inverter was an emitter follower, so it didn’t invert voltage."
This comment will be of interest to our ASR 33 clinic folks:
"Chain printer technology was later adopted by General Electric for the Terminet terminals and by Teletype for the Model 40 21.”
"21 Brodrueck patent No. 3,845,710, Nov. 5, 1974"
Happy New Year/Decade! :))
From Michael Albaugh, - Dec 31, 2019 11:22 pm
> On Dec 28, 2019, at 9:02 PM, Robert Garner wrote:
> Interesting — thanks for finding/posting excerpts from Jim Haynes’ “An Engineer's Memoir of Teletype Corporation."
Indeed. I do want to point out that Jim Haynes also edited the "Open Channel" for a magazine (Datamation?) and taught at U.C. Santa Cruz. He's quite a Gentleman and a Scholar. (and yes, _very_ knowledgable about Teletypes)
> I’m not sure what the author meant here by: “each stage was a voltage inverter but not considered to invert the signal logically”
> and “A logic inverter was an emitter follower, so it didn’t invert voltage":
I read it as meaning that by alternating the relation between voltage and logic level('A' gates used, say, +6V as logic 1 while 'B' gates used +6 for logic 0). I did something similar (albeit much less complex) when running 4000-series CMOS "upside down" in a piece of telcom gear, so a normal NOR gate, when run between Vss at ground and Vdd at -V became a NAND gate, and ViceVersa. A non-(voltage)-inverting gate would be a logical inverter just by virtue of its place in teh alternating chain of gates.
> This comment will be of interest to our ASR 33 clinic folks:
> "Chain printer technology was later adopted by General Electric for the Terminet terminals
I gave away my Terminet (and flexowriter), and can't even find the guy to see if he still has them and is looking to dispose of them. I have been told that they were a bear to keep running. The "chain" was more like a belt with metal type-teeth embedded in it, and there was a carriage with some number (7?) of hammers that slid along the width of the carriage. So it could not print an entire line "at once", but could print several characters that were close together quite quickly.
> and by Teletype for the Model 40 21.”
> 21 Brodrueck patent No. 3,845,710, Nov. 5, 1974
Hmmm, I'll have to look that up. The weirdest TTYs I've seen were the Inktronic and the machine (I forget the number) that "ate" normal start/stop tty codes and "excreted" a sort of "dot matrix" signal very like a HellScreiber, pretty much all mechanical. Imagine if a model 14/15 and a fax machine had a one-night stand and...
> Happy New Year/Decade! :))
"The Future Starts Tomorrow!" (Yoyodyne corp slogan)
From J. H. McCarthy, - Jan 01, 2020 11:28 am
Ed: Not sure I follow all this, but the 2 SMS emitter followers used in the 1401 design were not logic inverters. The out put(s) simply followed the input and provided more drive current than the input, and the voltage output swings were some what less. There was a P to P and U to U versions. ---- Jud
Justin (Jud) McCarthy
251 SW 9th Ave
Boca Raton, FL 33486
From Rick Dill, - Jan 01, 2020 12:26 pm
OK, let me come in on this. I knew the people in the early circuit group under Joe Logue in the 1401 era. They developed families of circuits for different logic functions and different circuit families.
The circuits which used carrier saturation in the base were separated by cost of the components for any logic operation and also by circuits which reduced the amount of saturation at cost of more transistors, diodes, and resistors. The latter had more cost and higher speed with the same transistors. These more or less correspond to the RTL (resistor transistor logic) and the TTL (transistor transistor logic) and got pretty well propagated around the industry in the days before integrated circuits. They also had equivalents in IC's in the early bipolar days. These circuits were generally able to have output levels that match the needed input levels, so they did not need intermediate level shifting circuits of alternating PNP and NPN circuits with input and output levels that matched the other of the pair.
At the high end was what IBM called the "current switch" and the rest of the world called "emitter coupled logic" or ECL. Hannon Yourke (if I got the spelling right) was the inventor of this circuit. In the earlier implementations this circuit did not include level shifting so that alternating PNP and NPN circuits were needed and the sequencing handled by the clock.
I don't know the details since I was working in devices and only got the generalities of the circuits guys working near me.
The 1401 was build for a low price entry and it certainly did not have ECL circuits. Whether there were places where alternating NPN and PNP circuits were required is something I do not know about.
What I do know is that the IBM alloy transistor design could be adapted to PNP and NPN simply by changing the materials used for the tiny spheres used for the emitter and base. Indium with a small amount of gallium was common for PNP transistors, but they could be made with mostly tin and a little bit of indium and/or gallium. The NPN couldn't use the indium or gallium dopants but needed antimony, arsenic, or phosphorus. The easiest of these would probably have been tin alloyed with antimony.
I will send a separate note on the evolution of uniform base alloy transistors to diffused base transistors. For IBM, it meant a significant speed increase from transistors that looked visually exactly the same as the transistors in the 1401.