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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.

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 3m 4 or 5 P-P 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 5m 4 or 5 P-P 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 5m 4 or 5 P-P Disks, Optical, scanners, cameras, mobile phones, memory sticks etc.
Ultra 2 SCSI 640 M bit/s 12m 68 Bus LVD (Low Voltage Differential) - high performance disks
1000base-T 1 G bit/s 100m 8 Bus Gigabit Ethernet - PCs, Network devices etc.
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
SATA-1.0 1.5 G bit/s 1m 7 P - P Serial ATA - high performance disks (AHCI). Uses 8b/10b encoding so data capacity is 1.5 /10 * 8 = 1.2 G Bit/s or 150 M Bytes/s
Ultra 320 SCSI 2.5 G bit/s 12m 68 Bus LVD - high performance disks
SATA II (2.0) 3 G bit/s 1m 7 P - P Serial ATA - high performance disks (AHCI). Uses 8b/10b encoding so data capacity is 3 /10 * 8 = 2.4 G Bit/s or 300 M Bytes/s
eSATA 3 G bit/s 2m 7 P - P Serial ATA - external connection (AHCI) Moving toward 6 G Bit/s. Uses 8b/10b encoding so data capacity is 3 /10 * 8 = 2.4 G Bit/s or 300 M Bytes/s
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.
USB 3.0 5.0 G bit/s 3 - 5m 5 P-P Cameras, PCs, Disk, optical etc. Uses 8b/10b encoding so data capacity is 5 /10 * 8 = 4.0 G Bit/s or 500 M Bytes/s
SATA III (3.0) 6 G bit/s 1m 7 P - P Serial ATA - high performance disks (AHCI). Uses 8b/10b encoding so data capacity is 6 /10 * 8 = 4.8 G Bit/s or 600 M Bytes/s
10Gbase-T 10 G bit/s 37 - 100m 8 Bus 10 Gigabit Ethernet - PCs, Network devices etc. Cat 6 - 37 to 55m, Cat6a - 100m.
Thunderbolt 10 G bit/s 3m 20 P - P Bi-directional. Developed by Intel and Apple for connection of Displays/Monitors and high-speed devices such as Discs. Devices may be daisy-chained (6 max). Uses Mini DisplayPort connector. Muxes DisplayPort and PCIe streams. Active optical cables (10+m) are under development. Power (10W) may be supplied over the cable.

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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