On OSes older than Win2000 the default max size is 2 Gigabyte AFAIK (Maybe there are some patches, most old-os users don't have them installed). You're on the save side when you keep the size under 2 gigs. I also guess BLitz has an internal limit of 2 gigs due to 32 Bit adressing. reading and writing such a file (eg 1.5 Gigs) may take some time, eg. half a minute or so.