To expand what Mrkvonic said, I found these by googling: 1) NTFS has to make 8.3 filesnames for every file (unless you tweak it via fsutil). Its gets progressively harder once your folder has a large number of files. Also applications that make the temp files, have to search for a unique name. I had a pokey old 4200 rpm drive, so each seek was very expensive, and lots of seeks were needed because (see point2) 2) Size of the MFT. The Master File Table can become many hundreds of MB in size and won't be cached as often (or atleast more of it will pbe paged out all the time). ntfsinfo from Sys Interals will give you the deets... 3) Each time the temp folder is enumerated - there's a lot more work to be done - esp. if you have a virus scanner that checks all the files in a folder, each time the folder is enumerated! I'd also been very aggresive with Windows Search indexing. Excluding the temp folder from the index, helped speed-up my computer too... EDIT: I also don't think registry optimizers(cleaning and defrag) do help much.