The DCR-SR21 has a Digital image stabiliser which is better than most camcorders that came out around the same time as it. Most video cameras that have been available for around the same time as it have an Optical image stabiliser. Some compact cameras have digital Image stabilisation only, which simply boosts camera sensitivity (ISO) to obtain a faster shutter speeds to help prevent blur. No hardware is involved.
A Digital image stabiliser is in fact the worst image stabiliser type across all small sensor size video cameras that are a comparable age to the DCR-SR21.
The best image stabiliser type amongst similar types of video camera is Optical.