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If flash memory is slower than magnetic disk, how can SSDs be faster than magnetic HDDs?

Flash memory (such as USB thumb drives) is a specific type of EEPROM, used for small portable disk drives. The difference is any byte of an EEPROM may be written, while flash drives are written by (larger) sectors. This makes flash memory faster than EEPROMs, but still slower than magnetic disks. (CISSP study guide by Eric Conrad etc.)

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    \$\begingroup\$ Who says that it's slower? I think you confuse the Flash memory architecture with flash drivers. In any case, you can compare the state of the art in both technologies, but it will depend on the maturity of the technology at the moment of the answer, nobody can say that it will be always true \$\endgroup\$
    – clabacchio
    Jun 14, 2012 at 8:01
  • \$\begingroup\$ @clabacchio CISSP study guide :) Quote: Flash memory (such as USB thumb drives) is a specific type of EEPROM, used for small portable disk drives. The difference is any byte of an EEPROM may be written, while flash drives are written by (larger) sectors. This makes flash memory faster than EEPROMs, but still slower than magnetic disks. \$\endgroup\$ Jun 14, 2012 at 8:18
  • \$\begingroup\$ Not true; flash memory is only erased in large sectors. And still your argument doesn't hold, because you compare two different things. SSD are sold because for consumer products are faster, maybe Google has some super-fast magnetic disks, who knows. Prove your claim \$\endgroup\$
    – clabacchio
    Jun 14, 2012 at 8:21
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    \$\begingroup\$ It is most likely out of date and needs updating. Back in the day that statement was true.. but things have moved on and the earth is not flat any more so to say \$\endgroup\$
    – Piotr Kula
    Jun 14, 2012 at 8:27
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    \$\begingroup\$ I'd say that they are wrong in any case: you don't make a statement so dependent on technology as an absolute truth, and without giving context nor data. \$\endgroup\$
    – clabacchio
    Jun 14, 2012 at 8:33

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The quote in the question is wrong. Thumbdrives use the same flash-chips as SSDs, but there are architectural differences.

In a high-performing SSD, you have maybe 8-16 flash-chips in parallel and a controller with a very wide interface that can access all chips simultaneously. This masks latency of the flash and of course makes the r/w rate much much higher than a single chip (and much higher than a magnetic disk).

See this image of a modern SSD PCB. There are as many chips on the bottom side as well.

In a thumb drive you might have a single flash only.

Also, apart from the hardware, due to the block-based nature of the flash and the fact that blocks wear out, the controller firmware is crucial in making the balance between raw performance and longevity. This is the most important difference between SSDs in performance. If it hadn't been for this, there would not have been such a huge market of SSDs and there wouldn't have been reports all the time that new designs fail and give abysmal performance after a while..

In a cheap thumb drive with much fewer chips in parallel the firmware might not be that thorough and can't hide for example erasure latency as well.

You also have the difference of the interface itself, USB vs. SATA, although in my experience this is not the limiting factor for slow USB thumb drive performance.

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A useful benchmark was carried out by notebookcheck.net which shows dramatic speed increases with SSD's. As @cybergibbons stated, though, interfaces can be the bottleneck, with USB flash drives being slower than SATA, for example.

enter image description here

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