Dan Wood made a review of the Commodore 1551/1541 disk drives. In this 20 minute video you can see the differences between the serial 1541 and the parallel 1551 disk drive. Dan also speak about OpenCBM and the XM1541 cable.
YouTube: http://www.youtube.com/watch?v=nVChSJ37kv4
Source: http://www.richardlagendijk.nl