February 18th, 2008

Vista SP1 vs. XP SP2 - Part Deux

Posted by Adrian Kingsley-Hughes @ 2:13 am

Categories: On the test bench, Vista

Tags: Result, Disk, Load, Operating System, Service Pack 2, Problem, Microsoft Windows Vista, Difference, Microsoft Windows Vista SP1, Test System

Following the benchmarks I carried out last week, I decided that the PC Doc HQ lab rats needed to pull a few all-nighters and carry out some more benchmarking tests on Vista SP1 and XP SP2.  Is it possible to determine conclusively which is the faster, more responsive OS?

One of the main criticisms of my initial benchmark tests was that I overlooked the fact that, under the hood, Windows Vista SP1 works differently to XP SP2 in the file copy department.  The difference is down to caching and how Vista carried out uncached I/O while XP caches the files.  On top of that is the further complication that the file transfer progress bars are coded to work differently.  Vista’s file copy dialog box goes away when the cache is committed, while under XP the copy dialog goes away while the committal is still pending.  In other words XP is coded to appear fast.  Mark Russinovich has the details:

Perhaps the biggest drawback of the algorithm, and the one that has caused many Vista users to complain, is that for copies involving a large group of files between 256KB and tens of MB in size, the perceived performance of the copy can be significantly worse than on Windows XP. That’s because the previous algorithm’s use of cached file I/O lets Explorer finish writing destination files to memory and dismiss the copy dialog long before the Cache Manager’s write-behind thread has actually committed the data to disk; with Vista’s non-cached implementation, Explorer is forced to wait for each write operation to complete before issuing more, and ultimately for all copied data to be on disk before indicating a copy’s completion. In Vista, Explorer also waits 12 seconds before making an estimate of the copy’s duration and the estimation algorithm is sensitive to fluctuations in the copy speed, both of which exacerbate user frustration with slower copies.

OK, so if this is the case XP has tricked us into believing that file copy is fast by sacrificing reliability for perceived performance.  In that case let’s put copy speed on one side for a while and try to look at this problem from a different angle.  Let’s consider responsiveness during large file transfers.  OK then, let’s benchmark the system while it’s performing file copy operations.

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