My 2GB dane-elec USB thumb drive is much slower in reading (and writing) data than a USB external hard disk. The hard disk is about 6 times faster. Is this normal? And if so, what is the reason that USB thumb drive is so slow while SSD drives are faster than hard disks?
This is normal, sort of. It all depends on the type of memory inside. USB flash drives are fast and really great at small file transfers. However, when you say "External USB drive", I take it as it's basically a regular hard drive connected via USB in an external enclosure. These types of traditional hard drives are slower than flash for small files, but as the file size increases, so does the appearance of speed: they can write more bulk data than a cheap USB Flash Drive.
Also, you should make sure that your cheapo USB flash drive is actually USB 2.0 compatible. If it's not, then USB 1.1 is wayyyy slower.
As far as SSD vs USB Flash drives, well it's what's inside that counts. You can actually get USB flash drives which are very fast.
Take a look at this article for a starting point.
EDIT : since everybody is saying the same thing, might as well i have some fun and say something different
What a question - so you expect small, shock-resistant, cheap... AND fast too??
The reason why USB drives are slower than mechanical hard drives and SSDs is simple - the manufacturers made them that way because it's a mass consumers product. And of all the feature-set, fast is the least appreciated by average consumers (they are not going to notice their single Excel document copied over 0.1 secs faster), and the most expensive to implement.
So, what do you think the manufacturers sacrificed? :)
while SSD drives are faster than hard disks
This is not necessarily true. They are much faster at randomly scattered small reads (which regular HDs are very, very, very bad at, since they involve waiting for mechanical parts to move before you can even start reading). But they are usually considerably slower at writing (since you have to erase flash memory before you can overwrite it) and even large bulk reading (which HDs excel at).
It's because SSDs tend to have much more advanced (and expensive) tech inside.
A typical SSD has a large amount of flash memory, combined with a controller that maps the ATA logical blocks onto various parts of the flash. In order to optimize performance, it will cache writes to combine them into single flash blocks. When logical blocks are overwritten, it will mark them as garbage and write the new data elsewhere (updating the logical-to-physical mapping, of course.) It will also run garbage collection in the background during idle time to coalesce blocks, optimize erase cycles and ensure that there are free blocks available to handle writes (so write operations don't have to block waiting for erasures.)
A cheap thumb drive, on the other hand, is a much simpler piece of hardware. In many cases, each logical block is hard-mapped to a fixed location in the flash memory. Or if they do have wear-leveling logic, it will be much simpler and without garbage collection. This makes the controller chip much simpler and cheaper, but with the side effect of much slower write performance and potentially a shorter lifespan.
Of course, there are plenty of different products in both spaces. Some SSDs (especially old models) are not very efficient or optimized, and some thumb drives (especially newer high-capacity, high-performance models) have a lot of logic used by SSDs, but the above comparison should be accurate when comparing a modern SSD against a bargain-basement thumb drive.