I've noticed that when Parallels 5 is doing heavy memory-intensive tasks (like deleting snapshots), it pages out to disk quote a bit. This paging normally happens when the system is running low on memory, but out of my 9GB of RAM, only about 3GB are being used. I looked in Activity Monitor, and noticed that the Parallels task running the cleanup of snapshots is not 64-bit. That strikes me as strange, as VMWare is touting their new 64-bit engine. If Parallels was running as a 64-bit app, it wouldn't have to be paging to disk, as it could be running these operation in memory. Any ideas as to when Parallels will be a 64-bit app?
