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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). This includes SCSI which may normally be shown in BYTES/SECOND. 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).

2. Distances are shown in meters, to convert to feet multiply by 3.28.

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)

4. Increasingly the PC/Laptop/Thingy industry is trying to reduce the number of interfaces offered to reduce real estate, complexity and - one hopes - decrease cost. For example, the new Thunderbolt interface is designed to allow connection of both monitors/displays and disc or other high-speed subsystems and USB supports just about every periperal known to we mere mortals.

5. High-speed interfaces used for graphic/media output to Monitors/Displays (including DVI, HDMI, DisplayPort) are described under monitors/displays.

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.

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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