Versions of Serial scsi.

SAS - serial attached SCSI - 
  Similar to SATA in that the protocols haven't changed but the physical 
  interface is a set serial connections that connect devices to hub rather 
  than a parallel bus.

  SAS is capable of recognizing and controlling SATA hard drives.

Firewire - IEEE 1394

  Serial version of SCSI created by Apple.

  4 data lines / 2 power lines

  480 Mb/sec 

  Data/Control transmitted in packets using RLL encoding.

  Hot plugable.

  Requires poling to detect addition of devices. 

  Controller card not actually needed. 

  Geared toward isosynchronous data transfers. Delivering data in a guaranteed
    time period - streaming video/audio.

  Faster than original Parallel SCSI

  Commonly available on external storage, newer versions faster than USB 2.0

  However, the emphasis of isosynchronous active makes it less than optimal
    for multidisk general storage (SAS better).

iSCSI - SCSI protocol implemented on top of tcp/ip. 

  Allows devices to uses standard network technology to interact. 

  While possible to actually do this over the internet, more commonly 
  implemented as an isolated network connecting only the SCSI devices and
  hosts.