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Thermal recalibration produces one unfortunate side-effect: if you attempt to access the disk while a recalibration cycle is taking effect, there is a slight pause until it completes. This does not cause any read or write requests to be lost, but it can cause a problem if you are performing a read or write task that is operating in "real time" and might be sensitive to the delay.

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First, let's give a brief explanation of what thermal recalibration is and why it would be used. As a hard drive operates, the temperature inside the drive rises causing the disk platters to expand (as most materials do when they heat up). In order to compensate for this phenomenon, the hard drive must periodically recalibrate itself to ensure the read and write heads remain perfectly aligned over the data tracks. Thermal recalibration (also known as "t-cal") is a method of re-aligning the read/write heads. During the operation of thermal recalibration, no data is read from or written to the drive.

For most applications, thermal recalibration is not a problem. However, it becomes cause for concern if you are using an application that requires a steady, uninterrupted stream of data. Such types of applications are generally audio/video programs used for digital audio recording, video editing and streaming, CD writing, etc. These applications require a sustained data flow and will not provide the desired results if a hard drive uses thermal recalibration.

Both Western Digital's EIDE and SCSI hard drives do not employ thermal recalibration. Instead, Western Digital uses embedded servo control, a mechanism that provides constant accurate feedback information to the head positioning system. Consequently, the drives are able to maintain an uninterrupted data stream and are very suitable for A/V applications.