I take it you are referring to the drive menu on windows installer, delete basically puts the drive partition to unformatted raw mode which is unusable until formatted again (Mainly used if you had multiple partitions that needed put them back to one drive again for whatever reason) Format sets the partition ready to be used for windows, clears all previous data from the drive and does the basic partition settings like the boot information and file system (NTFS) etc. Quick format is as it states is a quick format which merely clears the file headers and marks any data to be wiped without checking the entire partition, hence much quicker but won't see any errors.