An interesting blog post from Microsoft Fellow Mark Russinovich:

Windows Vista SP1 includes a number of enhancements over the original Vista release in the areas of application compatibility, device support, power management, security and reliability. One of the improvements highlighted in the document is the increased performance of file copying for multiple scenarios, including local copies on the same disk, copying files from remote non-Windows Vista systems, and copying files between SP1 systems. How were these gains achieved? The answer is a complex one and lies in the changes to the file copy engine between Windows XP and Vista and further changes in SP1. Everyone copies files, so I thought it would be worth a dive deep into the evolution of the copy engine to show how SP1 improves its performance.

Copying a file seems like a relatively straightforward operation: open the source file, create the destination, and then read from the source and write to the destination. In reality, however, the performance of copying files is measured along the dimensions of accurate progress indication, CPU usage, memory usage, and throughput. In general, optimizing one area causes degradation in others.

During Vista SP1’s development, the product team decided to revisit the copy engine to explore ways to improve both the real and perceived performance of copy operations for the cases that suffered in the new implementation. The biggest change they made was to go back to using cached file I/O again for all file copies, both local and remote, with one exception. With caching, perceived copy time and the publishing scenario both improve. However, several significant changes in both the file copy algorithm and the platform were required to address the shortcomings of cached I/O.

One final SP1 change worth mentioning is that Explorer makes copy duration estimates much sooner than the original Vista release and the estimation algorithm is more accurate.