I've been using Windows 7 for several years now, and always noticed that the copying speeds can be consistently relied on to drop throughout the task of copying files or folders. Today, I decided to test it.
I used five files ranging from 1GB to 8GB, copying them from one place to another on the same HDD - a SATA 3 (6.0 Gb/s) drive, but limited to SATA 2 (3.0 Gb/s, or 375MB/s) speeds because of the motherboard headers.
All of these five files started out copying at roughly 100MB/s, and proceeded to drop throughout until they'd eventually reached half of that by the end of the operation, with some ending up as low as 40MB/s.
Here's a benchmark for the drive:
Although I was surprised at the low rates for the random tests, the sequential rates seem more than adequate to sustain 100MB/s for copying, which I believe is a sequential operation so long as the drive isn't fragmented.
Given this, why is Explorer's copy speed always decreasing from the moment the copy operation starts?
Is this simply an unavoidable quirk of Windows 7, or is there an issue somewhere that I can address to solve it?
Edit: The drive I used for the above tests and benchmarks is a 2TB Seagate Barracuda, but I've noticed this behaviour with Windows 7 across many other drives and USBs for several years, so I'm convinced it's an OS problem rather than a drive one. The reason I included the benchmark was to illustrate that it's capable of drawing those speeds.