A The speed at which files can be copied from from one directory to another on the same drive.
The AS SSD benchmarking program was recently developed specifically for benchmarking SSD's. The utility is able to take several measurements that are well suited to solid state drives. One of the tests, ISO copy, is also relevant to slower storage devices including flash drives. The ISO copy test places two large 500MB files in a folder on the drive and then times how long it takes to copy the folder to another location on the same drive. The result is reported in both MBps and time taken. It's a real-world test that gauges a drives ability to read and write at the same time. Drives that have a good balance between their read and write speed fare relatively well on this test. There is further information, including instructions on how to use it to benchmark your own drive, on the AS SSD wiki page.

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