system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are USB Flash Drives so slow if SSDs are based on the same technology?

I know SSDs uses a different kind of Flash Memory, but regular USB flash drives are even slower than ordinary HDDs, and costing much more per GiB.

So, why they're so slow if SSDs are so fast (and vice-versa)?
gpt
The main cause of speed differences are the controllers. The controller allows the storage on the drive to talk to your computer. If the controller is not fast enough the speed of the connection to your computer does not matter. This is why an external USB hard drive will be faster than a flash drive. However, you can buy flash drives which have SSD grade controllers on them and transfer very quickly, but they cost a lot more. 

As for the cost factor, there are two major things which affect storage costs. The first is the cost of the controller, and the second is the cost of the storage chips. A 256 GB flash drive will have 256 GB of storage in a very compact space. However, a 256 GB SSD will have more room for the storage, reducing its cost because there are (for example) 32 8GB chips instead of 2 128GB chips on the flash drive. However, the more expensive controller on the SSD increases the cost compared to the low cost flash drive controller.