0
\$\begingroup\$

USB keys and SSD use the flash technology for their memory ; I don't have a great knowledge in electronic but I think RAM modules use this same technology. Could you tell me if I'm right please ? More precisely : do you know if the flash used by RAM modules (if it's the case) is totally the same than USB/SSD's one or if it's a bit different ?

If RAM modules use exactly the same Flash than USB and SSD, it would be possible to use these hardwares rather than RAM modules no ? (if USB ports are replaced with other stuff)

\$\endgroup\$
2
1
\$\begingroup\$

No, they don't.

DRAM cells are real tiny capacitators directly connected to the addressing logic, which makes them really really fast, but make them leak much, so they have to be refreshed thousands of times in a second. This is done by reading out data and rewrite the full load. Today's DRAM chips do that internally and fully automatical.

Flash ROM cells in contrary are somewhat bigger capacitators which are indirectly connected to the addressing logic. Their floating gate, which stores the information in the cell, is embedded into an isolating patch. So a Flash ROM cell leaks much less than a DRAM cell, it needs years until the information is jumbled by the leak. However, it's hard to empty or refill the cell through the isolator as needed to write a 0 or 1 into it. that's the reason why Flash ROM is much much slower to write than a DRAM cell. Reading speed is similar.

Analogy:

  • DRAM cell: glass of water (or no water)
  • Flash ROM cell: glass of water (or no water) with a lid and a very tiny hole in it.
\$\endgroup\$
1
\$\begingroup\$

RAM is completely different. The RAM you find in most computers is dynamic RAM (DRAM) and it is volatile memory - i.e. it loses its contents when the power is removed. DRAM stores data inside of very small capacitors. The simple construction of the memory bit cells means that it can be made at a relatively high density. The capacitors are so small that the stored charge leaks away and the entire contents of RAM have to be read out and written back many times per second. Read operations are also destructive as the capacitors have to be discharged to measure the stored charge, so read operations must be followed by write operations internally so no data is lost. Incidentally, magnetic core memory also has destructive reads. Since charging and discharging capacitors is a relatively fast operation, DRAM ends up being a reasonably high performance method of storing data. It also uses a high performance bus on the motherboard to interface with the CPU. DDR4 DRAM modules story about 19 gigabytes per second of bandwidth. Compare this to about 0.6 gigabytes per second for USB 3, 0.75 gigabytes per second for serial ATA, and 1 gigabyte per second for per lane of PCIe gen 3. As you can see, if you replace RAM with an ADD or a flash drive, the system performance will necessarily fall off a cliff.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.