Tech Stuff - PC Interface Speeds

We get pretty confused about all those interfaces being used on PCs (truth be told we get confused about lots of things). This table is designed to provide a quick overview.

Notes:

1. We have normalised all speeds to G (giga), M (mega) or K bits per second (written as bit/s using the ITU standard). To convert to bytes per second divide by 8 - except for serial connections where you should divide by 10 (assuming async 1-8-1 format). This includes SCSI which may normally be shown in BYTES/SECOND.
2. Distances are shown in meters to convert to feet divide by something!
3. The column marked Type defines the topology of the interface and may be:
   • P-P - Point to Point
   • Bus - shared bus
   • MD - Multi-Drop (master/slave)

Thanks: Dave Howell generously spent some time to update our pathetically small SCSI knowledge base. Many thanks. The information is courtesy of Dave any errors are courtesy of us.

Interface	Speed	Distance	Pins	Type	Use
Serial Port	1.2 - 115K bit/s	5m to 100m	9 or 25	P-P/MD	Serial Mice, Modems, Printers etc.
USB 1.x (Low Speed)	1.5 M bit/s	?	4 or 5	?	Mice, Keyboards, printers etc.
10base-T	10 M bit/s	100m	4 - 8	Bus	Ethernet - PCs, Printers, Network devices etc
USB 1.x (High Speed)	12 M bit/s	?	4 or 5	Bus	Mice, Keyboards, printers
SCSI	40 M bit/s	6m	50	Bus	SE. Disks, Optical storage
Fast SCSI	80 M bit/s	3m	50	Bus	SE. Disks, optical storage
100base-T	100 M bit/s	100m	4 - 8	Bus	Fast Ethernet - PC, Printers, Network devices etc.
Fast Wide SCSI	160 M bit/s	3m	68	Bus	SE. Disks, optical storage
Ultra SCSI	160 M bit/s	3m	50	Bus	SE. Disks, optical storage
Ultra Wide SCSI	320 M bit/s	1.5m	68	Bus	SE. Disks, optical storage
IEEE 1394a-2000	400 M bit/s	4.5m	4 or 6	?	Firewire/i.Link - disks, optical, scanners, camcorders etc.
USB 2.0	480 M bit/s	?	4 or 5	Bus	Disks, Optical, scanners etc.
1000base-T	1000 M bit/s	100m	4 - 8	Bus	Gigabit Ethernet - PCs, Network devices etc.
Ultra 2 SCSI	640 M bit/s	12m	68	Bus	LVD - high performance disks
FC-AL	1.0625 G bit/s	30m	8	Loop	Fibre Channel. Copper/coax. Max of 126 devices allowed.
FC-AL	1.0625 G bit/s	500m	N.A.	Loop	Fibre Channel. Fiber. Max of 126 devices allowed.
Ultra 160 SCSI	1.280 G bit/s	12m	68	Bus	LVD - high performance disks
Ultra 320 SCSI	2.5 G bit/s	12m	68	Bus	LVD - high performance disks
IEEE 1394b	3.2 G bit/s	100m	4 or 6	?	Firewire/i.Link - disks, network storage, digital video. Initial version is limited to 800 M bit/sec.

SCSI Notes:

These notes are all courtesy of Dave Howell - many thanks:

1. SE is Single Ended.

2. SCSI Cable distance is total including all cables, connectors etc.

3. The rapidly shrinking cable lengths is why "Differential SCSI" was developed. Rarely seen is the old High-Voltage Differential. Any of the above standards could be done as HVD, in which case the total cable length (at any speed) is 12 meters with multiple devices, or 25 meters if it was point to point.

4. The same distances (12/25meters) apply to LVD, Low Voltage Differential SCSI. This is the ONLY interface used with the more recent devices. Everything that's Ultra2 or beyond is LVD, and is Wide.

5. "SCSI-1," " SCSI-2," and "SCSI-3" refer to instruction sets, NOT interfaces. You can run a SCSI-3 drive on an antique interface: it will do non-fast non-wide SCSI. It's possible to have a SCSI-3 drive that is not "ultra," but just Fast SCSI, as well.

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