generic hexadecimally numbered files and directories starting with file00000000.chk and dir_00000000.chk respectively. On Windows NT family, a standard CHKDSK scan consists of three phases of testing file metadata. It looks for errors but does not fix them unless it is explicitly ordered to do so. The same applies to surface scan—this test, which could be extremely time-consuming on large or low-performance disks, is not carried out unless explicitly requested. CHKDSK requires exclusive write access to the volume to perform repairs. Due to the requirement of the monopolized access to the drive, the CHKDSK cannot check the system disk in the normal system mode. Instead, the system sets a dirty bit to the disk volume and then reboots the computer. During the Windows start-up, a special version of CHKDSK called Autochk (a native mode application) is started by the SMSS.EXE and checks and attempts repairing the file system if the dirty bit is set. Because of the exclusive access requirement and the time-consuming nature of CHKDSK operation, Windows Vista implemented a new file system health model in which the operating system fixes errors on the volumes as it encounters them. In the event that the problem is grave and a full scan is required, Action Center notifies the user to take the volume offline at the first convenience. Windows Vista and Windows Server 2008 added self-healing ability, turned on by default, in addition to providing the CHKDSK command. It detects physical file system errors and silently fixes them on the fly. Thus, many problems previously discovered on running CHKDSK never appear. It is administered by fsutil repair command. Criticism has been aimed at the tendency of AUTOCHK to automatically modify the file system when not explicitly solicited by the user who may wish to back up their data in prior, as an attempted repair may scramble, undermine and disown file and directory paths, especially on a multiboot installation where multiple operating systems may have interferingly written to the same partition. The alleged Windows 7 bug Before the release of Windows 7, InfoWorld reported an alleged memory leak in CHKDSK; according to the report, the chkdsk /r command would cause the memory consumption to reach the maximum and the system to crash. Randall C. Kennedy of InfoWorld attributed the original report to "various Web sources" and said that in his tests, the memory consumption reached above 90%, although he did not experience