I have been trying to find information on this but havent found it in the forums.
I suspect that the program, when you start a download reserves the amount of space on your HD sufficenet for the download.
About 5 months ago i had deleted bitcomet but last week i noticed that there was a 2.3 gig chunk of space used in temporary interenet files in my local documents, that could not be deleted or found. the folder itself is empty, even when i select view hidden documents. At first i figured it was some random thing micrshaft does for reserving temp files. A few days ago i tried to defrag my HD and the system found a large file, aproximatly 2.3 gigs that needed to be defraged but was unable to do so. upon displaying the file, it was a file i was trying to download using bitcomet about 6 months ago but never finished. Search cannot find the file or any part of it. I have now reinstalled bitcomet but it cannot find the file either. So basically there is 2.3 gigs of space used up on my HD that is in limbo now. how can i get rid of it?