Lamarr invented "frequency hopping" while CDMA cellular and GPS use "direct sequence". Frequency hopping is just what it sounds like: a narrowband transmitter is continually retuned to a different radio channel. Unless the receiver tuning follows the same sequence at the proper times it cannot receive the transmission.
Direct sequence XORs a narrowband signal with a high speed pseudorandom "chip" sequence, and the receiver undoes this operation by XORing it again by the same sequence properly synchronized in time. It closely resembles a keystream-type encryption system, though the "keystream" is not necessarily secret. The main difference is that direct sequence is a wideband signal while, at any instant, a frequency hopped signal is still narrowband.
Each method has advantages. Frequency hopping can be especially resistant to strong narrowband jamming, so it's a favorite of military systems (Lamarr's intended use). Direct sequence is easier to use with coherent modulation so it tends to use transmitter power more efficiently, and it can often provide precise timing and positioning as a side benefit. Or, in the case of GPS, as its primary purpose.
While CDMA mobile phones were very important in the 1990s and 2000s, it is now being replaced with LTE (Long Term Evolution), which uses OFDM - Orthogonal Frequency Division Multiplexing. So do many other modern terrestrial digital communication systems including DSL, HD Radio, DVB-T (but not ATSC), WiFi and DRM (Digital Radio Mondiale).
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There were two main types: the drum printer and the chain printer. The drum printer was cheaper and therefore much more common. The drum, which contained all the characters in a given font, rotated once for each row printed. An entire row was printed simultaneously; a separate solenoid-driven hammer in each column fired at the right instant to print the desired character in that column. You could easily tell from across the room whether your program had failed to compile or if execution ended with a core (!) dump. The burst pages between jobs had their own highly characteristic sound.
A related sound is that of ripping fanfold line printer paper to separate jobs. Who uses any kind of fanfold paper these days? Or even paper...?
Oh, and let's not forget the sound of the Hollerith (IBM punch card) reader...
It is contrary to reasoning to say that there is a vacuum or space in which there is absolutely nothing. -- Descartes