Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Oct 28, 2005 13:53:21 GMT -4
Mechanical sequencers where the norm until just recently. The projects I worked on in the 1980s were all controlled with sequencers as Count Zero describes -- a rotating drum with cams attached to a synchronous motor. The position of the cams could be arranged in such a way that each would trigger a specific switch at the appropriate time. The switch would then initiate the required action. They were very simple but worked great. Today they have been largely replaced by PLCs (programmable logic controllers).
Many young people today can't seem to think beyond their own little world. They believe that tasks performed by a certain technology today were undoable before the current technology was available. Just because they lack ingenuity doesn't mean their ancestors did.
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Post by JayUtah on Oct 28, 2005 17:40:02 GMT -4
Mechanical sequencers where the norm until just recently.
And I still enjoy making them just for the sheer joy of designing them. Not only are they highly reliable, they're fun to watch work.
I love showing people the drafting methods used to lay out cams. It's an art. I've got some old photographs somewhere of some of the original camshafts used in Pirates of the Caribbean and other audio-animatronic figures. There are simple cams that just open and close switches, but for purely mechanical systems there are elaborately-shaped cams that work together to create an enormously complex ballet of mechanical movement.
The Saturn V launch sequencer, by the way, was a mechanical cam-based system.
Many young people today can't seem to think beyond their own little world.
True, but the sharp young people today can think beyond my little world. There are closed-minded old people who can't be brought into the modern world, and there are closed-minded young people who can't appreciate the genius of the past. It doesn't have much to do with what generation you belong to; it's all about how much you're willing to learn.
Just because they lack ingenuity doesn't mean their ancestors did.
Right -- because it's a different kind of ingenuity accomplished with a different set of tools and a different philosophy of problem-solving, it can sometimes escape attention. A very good example of excellence in purely mechanical engineering is the Linotype typesetter. Study the design of one of those, and you'll realize just how brainy people can be. Another good example is IBM's punch-card technology. Long before digital computers used them, IBM marketed a whole bunch of electromechanical business machines for managing data using simple processes (collation, sorting, etc.) on punched cards.
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Post by ottawan on Oct 28, 2005 17:46:55 GMT -4
I enjoy reading your posts guys because it helps me learn more about the past that I lived through and that I witnessed.
Being a history and english major there are many scientific things that still confound me.
I think it was Bob who commented that the younger generation have a problem with equating a computer with a PC. I liked that observation.
One term has eluded me, though I must admit I have not done a lot of research on it.
What, exactly, is "core-rope technology"?
I hope I got the phrase right.
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Post by JayUtah on Oct 28, 2005 18:16:22 GMT -4
Computer memory can be considered erasable and non-erasable, as well as persistent or volatile. Today's microchip memory is generall erasable and volatile. Erasable means you can change what is stored in it. Volatile means something has to be sustained -- in this case, electrical power -- in order for the memory to retain its contents. A CD-ROM is non-erasable and persistent. You can't change the contents and you don't have to do anything special to keep it from losing its memory. In Ye Ancient Tymes, ca. 1960, erasable computer memory was also persistent. It was made of a lattice of electrical wires at whose intersections was placed a small piece of magnetic material. By manipulating the current in the wires, you could force the material -- the magnetic "core" -- to take on a certain magnetic polarization that could represent an "on" or "off" state -- the basis of binary storage. Manipulating the wires in other ways would let you read the state of each core. "Core memory" then was the erasable portion of a computer's memory. You would use that to store values that had to change during the life of the program, such as how far toward the moon you had gone, how much fuel was left in the tanks, or whether the digital autopilot should operate in "loose" or "tight" mode. If you leave out the wiring that lets you change the state of the core, and if you thread the "sensing" wires through some cores and not others, this would produce core memory that would contain a preset pattern of bits. You could hard-wire the pattern of bits that corresponded to a computer program and then that portion of memory would function as a read-only section of memory from which programs could be run. Erasable cores tend to look like grids. Non-erasable cores have a bit more random-looking wiring, and to some people resemble rope. See here for some illustrations that don't fit into the forum. hrst.mit.edu/hrs/apollo/public/visual3.htmSo a "rope core" or "core rope" simply means the type of memory whose contents were hard-wired in at the time of manufacture. In modern computers, the rope core corresponds to the ROM chips -- the ones that hold the elementary programs needed to get the computer going when it is first started up.
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Post by ottawan on Oct 28, 2005 18:23:59 GMT -4
Thanks Jay!
From what I glean from all of that is that what used to be stored in a single room now resides inside a chip!
This will help me try to explain to my nephews friends how the technology allowed us to go to the moon.
I have tried to lead them here and elsewhere but it is like flogging a dead horse.
Thanks again.
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Post by JayUtah on Oct 28, 2005 19:35:55 GMT -4
The most powerful computers in the 1960s took up entire rooms. The most powerful computers today still take up entire rooms -- they just have more capability. So yes, it depends on what you want out of the computer. In 1969 you could get a PDP-7 or a PDP-11 minicomputer. That was about the size of the Apollo guidance computer but a bit more powerful. The AGC was about the size of the biggest suitcase you can get into the overhead bin on an airliner. Today that same functionality can be had on a single chip -- and a very inexpensive chip at that.
The first version of the AGC took up three full-sized equipment racks -- say, three phone booths. That's because it was built from transistors and diodes that you'd buy at Radio Shack. Subsequent versions got smaller because instead of the little basic components they started using integrated circuits. You can build a basic logic gate -- sort of the Lego piece of digital logic -- with four transistors, some diodes, and handful of resistors. You could probably squeeze that into the space of a postage stamp. (In fact, that's how IBM made its first "integrated circuits".) But if you use the new photographic etching process, you can eliminate all the "packaging" (the colorful cases and little dangly wire bits) from those other components. In that same postage-stamp sized space you could now fit several gates. And when you start using custom-designed circuit boards instead of the "breadboards" used to build prototype circuits, you can shrink it down more.
You can still get the same kinds of logic circuits on chips that the AGC was built with. If you went down to Radio Shack and bought some NAND gates as microchips, you could build an AGC and it would still take up about the same amount of space today. But today we can put more on a single chip, and it makes business sense to do it because you're going to sell 88 billion of them. But there were only about 100 AGCs built, and even if it's physically possible to put all the gates and such on a single chip, it would have been horribly expensive to do it for such a small production run. Of course it wasn't physically possible in 1965, but you can hopefully see how you can get a certain amount of shrinkage just as a natural consequence of proceeding with the design. Because of how electrical engineers work, their initial mockups and prototypes are huge, having been built from large general-purpose components until they get the behavior right.
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Post by Kiwi on Oct 28, 2005 19:51:56 GMT -4
It's a pity that such excellent information about the Apollo computers should be hidden away in a thread about Bart Sibrel updating his website. I have started another, "Apollo Computers," in The Reality of Apollo. apollohoax.proboards21.com/index.cgi?action=display&board=apollo&thread=1130542838From the Apollo 15 Flight Journal: [It's important to realize that although the computer is a critical part of the spacecraft, it isn't an absolute requirement for its operation. Early in the development of the computer, there were even serious doubts that it would remain functional for the entire mission! As a result, Apollo was designed to be flown without an operational computer. All the tasks that it normally manages could be done manually. (Making attitude adjustments, firing the engine, etc.) An essential design philosophy: Always try to have survivable options even when a critical piece of equipment fails.]...Many young people today can't seem to think beyond their own little world. They believe that tasks performed by a certain technology today were undoable before the current technology was available. Just because they lack ingenuity doesn't mean their ancestors did. Music boxes with their spiked drums and clockwork mechanisms are wonderful examples of ingenuity from pre-electricity days. <Fixed typo.>
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Post by ottawan on Oct 28, 2005 20:24:28 GMT -4
Again, thank you gentlemen.
Ammunition to bring the children into the fold.
They do trust those who know of what they speak.
Fox airs the other view.
Such is life.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Oct 28, 2005 20:28:56 GMT -4
Many young people today can't seem to think beyond their own little world.True, but the sharp young people today can think beyond my little world. There are closed-minded old people who can't be brought into the modern world, and there are closed-minded young people who can't appreciate the genius of the past. It doesn't have much to do with what generation you belong to; it's all about how much you're willing to learn. Absolutely, there are people of both types in every generation. I didn't mean to imply only young are this way, or that all young people are this way. Long before digital computers used them, IBM marketed a whole bunch of electromechanical business machines for managing data using simple processes (collation, sorting, etc.) on punched cards. We were still using punch cards when I was in college; what a pain in the neck that was. It worked though. Perhaps Lunar Orbit can move the posts to the new thread. LO, do you have that ability with ProBoards? Music boxes whith their spiked drums and clockwork mechanisms are wonderful examples of ingenuity from pre-electricity days. This is a very good example of just the type of thing I was talking about. I wonder how many young people today have seen a working player piano? We had one in my family, in fact, my father restored it to working condition. It was fascinating to see how it operated.
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Post by ottawan on Oct 28, 2005 21:01:29 GMT -4
Player piano's!!!
Bob, thanks to one of them I learned how to sing "Bicycle built for two".
Daisy . . Daisy . . . give me your answer do . . . . . . .
Yikes.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Oct 28, 2005 21:33:56 GMT -4
♫ ... I'm half crazy, all for the love of you ... ♫Please humor me and pretend like I have a good voice.
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Al Johnston
"Cheer up!" they said, "It could be worse!" So I did, and it was.
Posts: 1,453
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Post by Al Johnston on Oct 29, 2005 10:27:39 GMT -4
I'm sorry Dave, I'm afraid I can't do that.
Dave, I think my mind is going...
;D
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Post by LunarOrbit on Oct 29, 2005 11:44:56 GMT -4
Perhaps Lunar Orbit can move the posts to the new thread. LO, do you have that ability with ProBoards? No, unfortunately Proboards software doesn't give me that ability.
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Post by drjohn on Oct 30, 2005 8:10:19 GMT -4
There is a book by Eldon Hall called "Journey to the Moon: The History of the Apollo Guidance Computer" You can find it here.
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Post by JayUtah on Oct 30, 2005 10:44:24 GMT -4
That's a great book; unfortunately Hall talks next to nothing about the software.
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