Delay-line memory

Delay-line memory is a form of <a href="/facts/Computer_memory/hQKVQ51J">computer memory</a>, mostly obsolete, that was used on some of the earliest <a href="/facts/Digital_data/JChckAvr">digital</a> <a href="/facts/Computer/SQe1aK05">computers</a>, and is reappearing in the form of optical delay lines. Like many modern forms of electronic computer memory, delay-line memory was a <a href="/facts/Memory_refresh/Wg1uQekt">refreshable memory</a>, but as opposed to modern <a href="/facts/Random-access_memory/DuD4bxh6">random-access memory</a>, delay-line memory was <a href="/facts/Sequential_access/8NCL847H">sequential-access</a>.
<a href="/facts/Analog_delay_line/Lg6MQ47b">Analog delay line</a> technology had been used since the 1920s to delay the propagation of analog signals. When a delay line is used as a memory device, an <a href="/facts/Amplifier/pnRgxncC">amplifier</a> and a <a href="/facts/Pulse_shaping/GrhYVMUJ">pulse shaper</a> are connected between the output of the delay line and the input. These devices recirculate the signals from the output back into the input, creating a loop that maintains the signal as long as power is applied. The shaper ensures the pulses remain well-formed, removing any degradation due to losses in the medium.
The memory capacity equals the time to transmit one bit divided by the recirculation time. Early delay-line memory systems had capacities of a few thousand <a href="/facts/Bit/S972NSaD">bits</a> (although the term "bit" was not in popular use at the time), with recirculation times measured in <a href="/facts/Second/jtFxnJXx">microseconds</a>. To read or write a particular <a href="/facts/Memory_address/7EsUmbea">memory address</a>, it is necessary to wait for the signal representing its value to circulate through the delay line into the electronics. The <a href="/facts/Latency_(engineering)/6Bjhn30H">latency</a> to read or write any particular address is thus time and address dependent, but no longer than the recirculation time.
Use of a delay line for a computer memory was invented by <a href="/facts/J._Presper_Eckert/G3bXAwdt">J. Presper Eckert</a> in the mid-1940s for use in computers such as the <a href="/facts/EDVAC/6DHxuu2d">EDVAC</a> and the <a href="/facts/UNIVAC_I/LQzozqY2">UNIVAC I</a>. Eckert and <a href="/facts/John_Mauchly/y6TeMdXU">John Mauchly</a> applied for a patent for a delay-line memory system on October 31, 1947; the patent was issued in 1953. This patent focused on mercury delay lines, but it also discussed delay lines made of <a href="/facts/Ladder_topology/B1lMjhKB">strings of inductors and capacitors</a>, <a href="/facts/Magnetostrictive/hkma4mTU">magnetostrictive</a> delay lines, and delay lines built using <a href="/facts/Drum_memory/yul0r8nG">rotating disks</a> to transfer data to a read head at one point on the circumference from a write head elsewhere around the circumference.

Delay-line memory open-in-new

Delay-line memory