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SRAM, DRAM, Flash, EPROM - all of the memory cells contain one bit of data each. Is there any memory cell that can store more than one bit, e.g. 2 bits/4bits?

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closed as too broad by Oleg Mazurov, Leon Heller, Finbarr, Warren Hill, Voltage Spike Sep 26 at 15:21

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    \$\begingroup\$ I don't know why you couldn't use google to find this. It sure came up very easy for me as the first link. Read it through. \$\endgroup\$ – jonk Sep 13 at 20:02
  • \$\begingroup\$ Short answer, yes \$\endgroup\$ – Voltage Spike Sep 26 at 15:21
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Yes. When you get down to the level of a memory cell, the circuitry is pretty analog. So you can store multiple voltage levels in the cell, and interpret those multiple levels as encoding more than one bit.

There are parts in production that use this.

Google "multi-level memory".

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    \$\begingroup\$ I don't think this is true, in general, and is at best misleading. SRAM memory cells use positive feedback so they can reliably store 1 bit. DRAM cells deal with significant charge leakage and have to be refreshed often just to hold one 1 bit per cell. Mask programmed ROM is inherently one bit per cell. Only Flash memory offers a practical way to store multiple bits per cell. \$\endgroup\$ – Elliot Alderson Sep 13 at 22:35
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    \$\begingroup\$ @ElliotAlderson consider that most of the memory cells that exist in the world are multi-level flash cells. \$\endgroup\$ – Chris Stratton Sep 13 at 23:49
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    \$\begingroup\$ @ChrisStratton Perhaps, but most of the types of memory cells are not multi-level cells, and this answer says that "a memory cell", without qualification, can store multiple levels. That is simply not true. \$\endgroup\$ – Elliot Alderson Sep 14 at 13:05
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Actually you’ll have a really hard time to find a NAND flash device that does not store more than one bit per cell nowadays. This is one of the reasons the price of memory cards and SSDs (in terms of $/GB) has dropped so dramatically over the years.

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  • \$\begingroup\$ And if you want one that only stores one, you pay for it. So much that there's an intermediate solution where they put multiple copies of the same bit in the multi-bit cell! \$\endgroup\$ – Chris Stratton Sep 13 at 22:10
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Of the semiconductor memories on the market, only some Flash EPROM technologies store more than 1 data bit per memory cell.

As an example, the Cypress Mirrorbit technology stores two data bit in a single Flash memory element, utilising four stored voltages to do so. You'll find details of those parts on the internet.

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