USB is the latest in the USB standard. You can plug USB 1 or 2 into a USB 3 port but it will transfer at slower speeds. The port can be identified by SS or a blue plastic insert.
Transfer Speed: 5Gbps
Maximum Length: 3m
There are different USB connectors and ports used for different devices. If the PC doesn’t have enough USB ports, a powered or non-powered USB hub can be used. You can daisy chain (plug into one another) up to 127 USB devices.
FireWire (IEE 1934)
FireWire (Apple) is also referred to as iLink (Sony) and Lynx (Instruments). There are two versions; FireWire 1394a and 1394b. You can connect two XP PCs together allow them to communicate with each other. You can also connect 63 devices together in a daisy chain, even if one device if off the others will still function as normal. There is also a FireWire Mini port used for devices such as Cameras.
Pins: 6 (FireWire) or 4 (Mini FireWire)
Transfer Speed: 400Mbps | 800Mbps
Maximum Length: 10m
There are different versions of SCSI; SCSI-1, SCSI-2, Ultra-SCSI, Wide Ultra-SCSI and many more. The 68pin female Ultra-320 port is the most common today.
Transfer Speed: Upto 320MBps
Maximum Length: Multiple