Reason while there is difference between copying of file from system (hard disk) to flash drive and writing of files from flash drive back to system (hard disk)

There is time difference between copying of file from system (hard disk) to flash drive and writing of files from flash drive back to system (hard disk) because system has disk in its compartment why flash has an integrated memory,

Data can be easily access from hard disk, which makes it faster to access data. So, writing of files from system (hard disk) to flash is always slow than writing of file from flash to system (hard disk).

Findings from the observation are line with the findings from Wikipedia which states that: Most USB flash drives had USB 2.0 connectivity, which has 480 Mbit/s as the transfer rate upper bound; after accounting for the protocol overhead that translates to a 35 MB/s effective throughput. That is considerably slower than what a hard disk drive or solid-state drive can achieve when connected via the SATA interface. 

Speeds may be given in megabytes per second (MB/s), megabits per second (Mbit/s), or in optical drive multipliers such as "180X" (180 times 150 KiB/s). File transfer speeds vary considerably among devices; typical fast drives from this generation claim to read at up to 30 MB/s and write at about half that speed, what is about 20 times faster than the theoretical speed USB 1.1 can achieve, which is limited to 12 Mbit/s (1 MB/s with accounted overhead). The effective speed of a device is significantly affected by the data access pattern; for example, small writes to random locations are much slower (and cause more wear) than long sequential reads.