When copying from USB or external drive, why does it starts very fast and suddenly drops transfer rate by up to 50% and stays there? Why it can’t be speed as in the beginning all the time?

Question

Is it a hardware limitation or calculation algorithm problem, until enough data is transferred to calculate exact speed?

In: 14

Answer 1

First the OS is filling the buffer by reading the data as fast as possible – and makes it look like it’s the speed of data transfer. But if the writes to the target drive can’t be performed as fast, the OS will also slow down the reads accordingly – and you’ll see the actual speed of the transfer. On SSDs and thumb drives writes are often slower than reads, while SSDs are usually faster than HDDs.