If I correctly understand, RAM and SSDs both use flash memory, though SSDs use NAND flash memory. RAM loses its data when unpowered. Why don't SSDs lose data the same way?
The short answer is that they aren't the same: RAM is volatile memory, whereas flash memory is non-volatile.
More specifically, the RAM in your PC is dynamic RAM, or DRAM. Each bit of DRAM consists of a transistor and a capacitor, which stores a bit of charge. The charge in a capacitor decays quickly, and so it must be continuously refreshed.
There also exists static RAM, SRAM. This uses latches to store data, so it doesn't have to be continuously refreshed, but power still needs to be applied. (Also, it is more complex and expensive, since it takes several transistors to make a latch for each bit of memory.)
Flash memory, on the other hand, uses floating-gate transistors for storage. NOR flash utilizes them somewhat differently than NAND, but the principle is the same. NAND flash is used for SSDs, because although it's slower, it's much more dense and cheaper to mass-produce.
Read full thread there.It gives vast informations into how various RAM devices work.