It should be noted that the effect of the value need not be continous. For example, a device might provide only two modes: one from 0 to 126 and other from 127 to 253. Per the specification, values of 127 and higher do not permit the device to spin down to save power.
Attribute values are used to represent the relative reliability of individual performance or calibration parameters. The valid range of attribute values is from 1 to 253 decimal. Lower values indicate that the analysis algorithms being used by the device are predicting a higher probability of a degrading or faulty condition.
Each attribute value has a corresponding threshold limit which is used for direct comparison to the attribute value to indicate the existence of a degrading or faulty condition. The numerical value of the attribute thresholds are determined by the device manufacturer through design and reliability testing and analysis. Each attribute threshold represents the lowest limit to which its corresponding attribute value can equal while still retaining a positive reliability status.
If the crit field is ``yes'' then negative reliability of this attribute predicts imminent data loss. Otherwise it merely indicates that the intended design life period of usage or age has been exceeded. The collect field indicates whether this attribute is updated while the device is online. The reliability field indicates whether the attribute value is within the acceptable threshold.