Delay line memory: 99 tubes of mercury on the wall...

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tinyterror
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Delay line memory: 99 tubes of mercury on the wall...

Postby tinyterror » Fri Nov 30, 2007 5:12 pm UTC

When someone says memory leak these days, they usually are referring to when a computer program loses track of memory that it allocated. Nobody actually takes the expression to mean a substance actually leaking out of the computer. Well, back in the 1940's the term memory leak had a far more serious meaning.

Ladies and gentlemen, I give you one of the earliest digital memory technologies out there, Delay Line Memory!

Image

See, this is the kind of thing I want attached to my computer. When people ask me what the hell it is, I can tell them SCIENCE!

In its simplest form, delay line memory consisted of a pipe filled with an acoustically conductive fluid medium such as mercury. On one end of the tube is a speaker (to generate pulses in the medium) and a microphone (to read the pulses from the medium). When one wanted to right a bit to the memory, a pulse was transmitted into the pipe. This pulse would travel down the pipe through the medium, taking a calculated period of time to reach the end, where it would be picked up by the microphone. These pulses could be stacked within the pipe, forming an extremely primitive SAM device. Yes, thats SAM, short for Serial Access Memory! As a pulse was read at one end of the tube, it would be changed to a new value or kept in its current state. The pulse would then be retransmitted into the tube again, preserving the value of a single bit.

With conventional modern memory, accesses can be made at any point in the memory. With delay line memory, you would have to ask for an address or a pulse number, then wait for the pulse to propagate through the tube. Once the pulse arrives at the reader at the end of the tube, it is accessible to the computer! In a way, this memory had the same access characteristics as a hard drive in that the computer must wait for the point on the drive that is storing the required data to spin into position. The access time for any particular bit in the tube was approximately 0.2 miliseconds. Thats faster than modern hard drives by about 20 times. This might sound pretty quick, but keep in mind that this stuff was used as RAM. Modern ram has access times in the nanoseconds.

Just to give you some idea of how much a pain in the ass acoustic delay line memory devices were to use, let us look at some of the physical specifications of the UNIVAC. According to wikipedia, the UNIVAC had a 1000 word memory. This required 7 memory units, each with 18 mercury columns. Each one of these columns was about 2 feet long. The memory units alone were the size of a small room for UNIVAC. In order to function properly, the mercury columns had to be kept at 40 degrees C, and required a full team of engineers to constantly tune them in order for the acoustic properties to be maintained. How's that for a crappy job? What do you do? Well, I tune giant pipes full of mercury all day long in a room that is over 100 degrees. Splendid!

Then again, kids in schools used to play with blobs of mercury in science class with their bare hands in the 50's. Truly these were the good old days!

For more info, see wikipedia: http://en.wikipedia.org/wiki/Delay_line_memory
Last edited by tinyterror on Thu Dec 06, 2007 5:17 am UTC, edited 1 time in total.

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Re: The memory is leaking again. Call HAZMAT!

Postby Axman » Fri Nov 30, 2007 6:23 pm UTC

Wow, I thought Stephenson made that shit up because he's all hard for pipe organs.
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Re: The memory is leaking again. Call HAZMAT!

Postby scowdich » Fri Nov 30, 2007 7:11 pm UTC

I also thought that Stephenson had invented a clever, but totally silly, device. Holy shit this is awesome.

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tinyterror
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Re: The memory is leaking again. Call HAZMAT!

Postby tinyterror » Fri Nov 30, 2007 7:21 pm UTC

Anyone care to refresh my memory as to where stephenson talked about this stuff? Its been a while since I really read any of his stuff.

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Re: The memory is leaking again. Call HAZMAT!

Postby scowdich » Fri Nov 30, 2007 7:25 pm UTC

Near the end of Cryptonomicon, Waterhouse (the '40s Waterhouse) invents a computer based on Turing's concepts to solve German and Japanese codes. As he's obsessed with pipe organs, his design for RAM (which he seriously considered painting a little ram's head on) heavily uses concepts of acoustics and resonance.

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tinyterror
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Re: The memory is leaking again. Call HAZMAT!

Postby tinyterror » Fri Nov 30, 2007 7:27 pm UTC

Ah, thats why I didn't catch the reference. Cryptonomicon never really did it much for me.

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Re: The memory is leaking again. Call HAZMAT!

Postby '; DROP DATABASE;-- » Fri Nov 30, 2007 8:16 pm UTC

tinyterror wrote:refresh my memory
*groan*
poxic wrote:You suck. And simultaneously rock. I think you've invented a new state of being.

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tinyterror
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Re: The memory is leaking again. Call HAZMAT!

Postby tinyterror » Fri Nov 30, 2007 8:17 pm UTC

'; DROP DATABASE;-- wrote:
tinyterror wrote:refresh my memory
*groan*


I am so, so sorry.


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