This latches ( Gated Latch, SR Latch, and Flip Flops) can only store memory IF there is electric current flowing, but everything will go OFF if no current.

I wonder how memory is stored in memories like SD Card, USB flash drive, etc. that the data stays even if removed to the device (that conducts electricity)?

  • 4
    \$\begingroup\$ Google keyword: EEPROM, Floating gate mosfet. \$\endgroup\$
    – Long Pham
    Jul 14, 2018 at 5:42

1 Answer 1


The data in modern EEPROMS are stored in tiny capacitors made of silicon, as the normal MOSFET transistors are made, just using two gates, one of which is "floating". But as should be understood, every capacitor has certain leakage, small, but... Therefore the data in flash memories have limited time for how long they keep the charge, called "retention time", typically 10-20 years, depending on quality of manufacturing and chip temperature. See, for example, this lecture for more details.

  • \$\begingroup\$ Mmm… there's a bit more to a flash memory cell than "normal MOSFET transistors". en.wikipedia.org/wiki/Flash_memory#Principles_of_operation has more details. \$\endgroup\$
    – user39382
    Jul 14, 2018 at 7:15
  • \$\begingroup\$ This is a very misleading answer. EEPROMs and flash memory are much different from dynamic RAM, which does in fact store information as charge on a capacitor. If you don't talk about floating gates and electron tunneling you are missing the big picture. \$\endgroup\$ Jul 14, 2018 at 12:05
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    \$\begingroup\$ @duskwuff, there is always "a bit more", I would say "quite a bit more". My answer was trimmed down to the level of question. And yes, a floating gate is a capacitor. In attempt to salvage my answer, I am adding the keyword "floating". \$\endgroup\$ Jul 14, 2018 at 15:06

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