40 lines
1.7 KiB
Markdown
40 lines
1.7 KiB
Markdown
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tags: [computer-history, memory]
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created: Wednesday, September 18, 2024
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# Delay line memory
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- First described in the _First Draft_ by #vonNeumann based on work by Eckert
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and Mauchley.
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- Information is stored as acoustic waves travelling through a medium, typically
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mercury. As sound travels more slowly than electric charge (light), if
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electric signals are converted to sound, the delay time involved can be used
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as a type of store.
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- It worked as follows:
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- Imagine we have an 8-bit number. The number is input as a sequence of pulses
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where a pulse is 1 and the absence of a pulse is 0.
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- The pulses are converted into sound waves (using a transducer, as with a
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speaker) and sent through a mercury-filled tube.
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- The length of the tube is calculated so that it takes exactly the time of
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one machine cycle for a pulse to travel from one end to the other
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- At the other end of the tube, another transducer converts the sound waves
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back to electrical pulses
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- This operates in a loop: the pulses go back into the input end of the tube
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and the cycle runs again.
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To read the data, the computer would "listen" to the pulses coming out of the
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receiving end. To write new data, the computer would inject new pulses at the
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precise moment when it wants to change a '0' to a '1' or vice versa.
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For an 8-bit number there would be 8 pulses for each bit and it would be
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necessary to keep track of 8 specific positions in the delay line where each bit
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would be stored.
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The limitations were timing - difficult to keep track of each precise bit and
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when it would arrive at the output. Also it was sequential rather than random
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access. Not every bit could be accessed at once, you had to wait for its time
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slot to come around to access it.
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