Each test file is filled with a coded number sequence (a Pattern) that is used to verify the correct operation of the disk when the file is verified (read). Files are created in the free space on the disk until the disk is at least 94%* full (we’ll refer to this as the ‘full’ level). When the disk has reached this limit, all the test files are deleted and the test starts again.
(*) 94% is used on disks that have a swap file or a Windows directory. A limit of 94% is used to ensure that some space is kept for use by other applications (including the windows swap file). On disks that do not have a swap file or a Windows directory, between 99.5% and 100% of the disk will be used.
簡單來說，在有OS系統檔的磁區下，預設會寫到94%滿，沒有OS系統檔的磁區，預設會寫到99%滿
Reference: BurnInTest help document
