One way that unreadable sectors may be created, even when the drive is functioning within specification, is through a sudden power failure while the drive is writing. Also, even if the physical disk is damaged at one location, such that a certain sector is unreadable, the disk may be able to use spare space to replace the bad area, so that the sector can be overwritten. More detail on the health of the drive may be obtained by examining the S.M.A.R.T. Attributes. S.M.A.R.T. Attributes were included in some drafts of the ATA standard, but were removed before the standard became final. The meaning and interpretation of the attributes varies between manufacturers, and are sometimes considered a trade secret for one manufacturer or another. Attributes are further discussed below. Drives with S.M.A.R.T. may optionally maintain a number of 'logs'. The "error log" records information about the most recent errors that the drive has reported back to the host computer. Examining this log may help one to determine whether computer problems are disk-related or caused by something else (error log timestamps may "wrap" after 232 ms = 49.71 days)  A drive that implements S.M.A.R.T. may optionally implement a number of self-test or maintenance routines, and the results of the tests are kept in the "self-test log". The self-test routines may be used to detect any unreadable sectors on the disk, so that they may be restored from back-up sources (for example, from other disks in a RAID). This helps to reduce the risk of incurring permanent loss of data. Many motherboards display a warning message when a disk drive is approaching failure. Although an industry standard exists among most major hard drive manufacturers, issues remain due to attributes intentionally left undocumented to the public in order to differentiate models between manufacturers. From a legal perspective, the term "S.M.A.R.T." refers only to a signaling method between internal disk drive electromechanical sensors and the host computer. Because of this the specifications of S.M.A.R.T. are entirely vendor specific and, while many of these attributes have been standardized between drive vendors, others remain vendor-specific. S.M.A.R.T. implementations still differ and in some cases may lack "common" or expected features such as a temperature sensor or only include a few select attributes while still allowing the manufacturer to advertise the product as "S.M.A.R.T. compatible."