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1956 Binary Desk Computer LIBRASCOPE LGP-30

S

snoopyyogi

New Member
Joined
Dec 12, 2016
Messages
3
Hey guys,

I have recently acquired an old Librascope LGP-30 computer. I've been told that this was the oldest computer in Vancouver, so it may be one of the oldest in Canada, or even North America.

Unfortunately, I don't know too much else about this. I have looked this up on wikipedia and have found that these were first manufactured in 1956 and were designed by one of the scientists who worked on the Manhattan Project.

It is currently located at my warehouse in Calgary, Alberta, Canada.

Haven't tried powering this on.

Might be interested in selling this, but if anyone has anything more they could tell me about it, I would also appreciate it!
 

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I wonder if the other box in the other picture is the drum.
It could be emulated with most any of the micro controllers
we have today though.
You'd most likely need some voltage translation.
Dwight
 
No, the drum's in the main unit; as you face it, it's on the upper right-hand side.

lgp30-2.jpg


The drum isn't actually very big; but note the huge motor underneath. I think that the second cabinet belongs to a high-speed paper-tape interface.
 
20161213_121648.jpg

Thanks for the links guys. Some very interesting info here. I was able to remove the front panel and take a photo of the inside of this as well.
 
Was able to open the top of this and take a few more photos of the inside, showing the drum, and one showing the serial number.

Please see attached.

20161216_124812.jpg20161216_124846.jpg20161216_124858.jpg
 
Very cool stuff! Note that one of the vacuum tubes visible in the first and second pics (last one down in the second pic) has 'gone to air' (lost its vacuum), as noted by the white top. Granted, something like that is probably the least of someone's worries when trying to power up a computer like this, but it's definitely something to watch out for.

As noted above, the LGP-30 is mentioned in "The Story of Mel", one of my favorite stories about the early days of the computer industry. I'm not entirely sure that Mel would appreciate the memory drum being replaced by emulation, since the position of the drum relative to the reading head seems to have factored into many of his programs! Anyway, the story can be read here.
-Adam
 
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AdamAnt316 said:
I'm not entirely sure that Mel would appreciate the memory drum being replaced by emulation, since the position of the drum relative to the reading head seems to have factored into many of his programs!
Click to expand...
The emulator I looked at (must have been a link from here, or somewhere) had the timing of the drum emulated as well.
 
The drum is the memory, a rotating magnetic drum. So how long it took to read a location of memory depended on where it was on the drum, relative to the reader. Each instruction in the LGP-30 had the address of the next instruction as part of the instruction. So when the current instruction had finished execution it's likely that the next position on the drum had already passed, so the address of the next instruction would be to somewhere else on the drum. So, if you looked at the program, the instructions wouldn't be sequentially in memory - instead they would be spread around, so that the next instruction to execute would be in just the right place (at least if you were Mel and optimised it that way). And Mel didn't bother with coding delay loops if one was needed, he simply placed the next instruction so that just the right amount of time had passed.
 
When I was a kid my Dad took me to work, and left me with an IBM field engineer for a while. The guy took time out to teach me how vacuum tubes work, and show me the innards of a malfunctioning drum memory being worked on. I still remember the bars with many r/w heads mounted on them, encircling the actual drum. It seems to me there were 100+ r/w heads. He said head alignment was a project! This was all hooked to the IBM vacuum tube computer at the AFB where my Dad worked, I think a 704 or 705.
 
Tor said:
The drum is the memory, a rotating magnetic drum. So how long it took to read a location of memory depended on where it was on the drum, relative to the reader. Each instruction in the LGP-30 had the address of the next instruction as part of the instruction. So when the current instruction had finished execution it's likely that the next position on the drum had already passed, so the address of the next instruction would be to somewhere else on the drum. So, if you looked at the program, the instructions wouldn't be sequentially in memory - instead they would be spread around, so that the next instruction to execute would be in just the right place (at least if you were Mel and optimised it that way). And Mel didn't bother with coding delay loops if one was needed, he simply placed the next instruction so that just the right amount of time had passed.
Click to expand...

Sometimes called "one plus one" addressing. The IBM 650 was another such system. Initially, there was an assembler (SAP: Symbolic Assembly Program) for it, then someone got the bright idea to let the assembler figure out optimum placement of instructions. SOAP was thus born (Symbolic Optimizing Assembly Program).

You didn't need a drum for this setup. The Packard-Bell PB 250 used magnetostrictive delay lines for memory, where memory was provided by the time it took a pulse to propagate down the nickel-alloy wire. More "One plus one" addressing. There were other such machines.
 
It may be worth mentioning that the magnetic drum was NOT a mass storage, rather operational mamory, more akind to todays RAM.
History of the early memory is realy fascinating.
 
alpher said:
It may be worth mentioning that the magnetic drum was NOT a mass storage, rather operational mamory, more akind to todays RAM.
History of the early memory is realy fascinating.
Click to expand...
Wouldn't it be more akin to core memory than today's semiconductor RAM? It'd seem that a magnetic drum wouldn't lose its contents automatically when the computer was turned off, unless there's some aspect of it I'm not aware of.

KC9UDX said:
Yes.

The fascinating thing about these schemes is how obvious our modern memory seems in comparison, but obviously how obvious it wasn't.
Click to expand...
Indeed, there were many attempts at memory storage in the early days of computers. To me, the most fascinating of these is the RCA Selectron, a vacuum tube which stored data electrostatically. It was used in only one computer, the JOHNNIAC, before being eclipsed by magnetic drums and other forms of memory. More info here and here.
-Adam
 
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