: eclectic content

Author: Lyberty
Article Date: 2002 Article last updated: November 2005;
(minor updates: 2007, 2008)*2
key: kilobit transfer speeds, megabit transfer speeds

USB speeds (vs. FireWire or LAN Ethernet)


Theoretical Maximums, Compared (in megabits per second):
USB High Speed is 480 mbps (megabits per second), aka million-bits-per-second. Also written 480Mbit/s.

USB now (2005) refers only to the 12 mbps (twelve mega-bits per second, aka "12Mbps" [view reference] )
and the 1.5 mbps portions of the USB 2.0 specification. These portions, often referred to as full-speed (FS) and low-speed (LS) respectively, or USB 1.1 and USB 1.0 respectively, should today be referred to simply as "USB." USB (including USB 1.1 and USB 1.0) is compatible with the USB 2.0 specification, meaning it works with USB and Hi-Speed USB systems, cables, devices and peripherals, not that it runs at those higher speeds. Because of this compatibility, some weasely manufacturers will apply the USB 2.0 description to their product, when what they mean is that the product is "compatible with USB 2.0".

In other words, USB 1.1 only supports LS/FS modes ; USB 2.0 supports LS/FS/HS mode.
When indicating the data transfer rate, the representation: 'FS', 'LS' or 'HS' could be used.

High-Speed USB logoSo unless the description says "High-speed USB" (or has a "Hi-Speed USB" logo, pictured at right), you should assume that the device will only run as 12 mbps, even if it says "USB 2.0".

Pay little attention to claims of "40 times faster than original USB 1.1". This label is often applied by people who don't know what they are talking about.

If you're the trusting type, you can assume USB 2.0 = 480 mbps max and USB 1.1 = 12 mbps.

The speeds associated with USB High-Speed and USB (480 mbps, 12 mbps, and 1.5 mbps) refer to the theoretical maximum speed of the USB interface on a USB device or USB port and really have nothing to do with the device itself. The actual speed a USB-compliant device achieves is not necessarily the speed of the USB specification (i.e. the "USB 2.0" specification) reflected in the product descriptions and marketing materials.
Real performance of any given product is dependent upon how fast that product can run. The device can only achieve the theoretical speeds if it can keep up with the USB data transfer rate. [from Understanding USB ]

Note also that FireWire (rated at 400 mbps) consistently tests faster that USB 2.0 (rated at 480 mbps) when data transfer is tested on a single device having both interfaces. [why?]
{note: FireWire 1394a = 400 mbps; but 1394b allows 400 mbps (S400), 800 mbps (S800), or 1600 mbps (S1600), and others. FireWire-800 is always S800.}

From GlyphTech:

"Even though USB 2.0 Hi-Speed has a theoretical max raw data rate slightly higher than FireWire (480 mbps vs. 400 mbps), the typical sustained transfer rates are about the same, because FireWire is a more efficient protocol to use in audio and video environments. In fact, in most cases, FireWire beats USB 2.0 Hi-Speed, albeit by a small margin. Very often it will be the computer or hard drive mechanism which limits the system performance more than the interface, so you might see about the same performance using FireWire-A or USB 2.0. "

According to NEC (Dec 2004):
"Specified speed of USB 2.0 is 480 mbps (in other words, around 60 Million Bytes per second, or 57.2 MB/s), but 57.2 MB/s is NOT the actual data rate.
This is because USB 2.0 packet is inclusive of overhead data.
[Note that conversion from megabits to MegaBytes requires (x*1,000,000/8)/1,048,576.]

Moreover, idle time are added between packets.
Besides, data rate is also dependent on the system architecture, the PCI bus and the attached USB devices.

Therefore, actual data transfer rate [of USB 2.0 High-speed] will be lower than 480 mbps (57.2 MB/s).
Our measurement result of data transfer rate with USB 2.0 storage device (HDD) is about 20 - 25 MB/s on average."

Ethernet: (per source)

About 50% of the 10 Mbps capacity can be used.
100 Mbit Ethernet -- Used within a building. The main standard is called 100BaseT. About 50% of the 100 Mbps capacity can be used. With switches, up to 99.9% of the capacity can be used.
1000 Mbit Ethernet, Gigabit Ethernet -- Used for backbones in buildings. The main standard is called 1000BaseT. About 50% of the 1,000 Mbps capacity can be used. With switches, up to 99.9% of the capacity can be used.
[this means that 100 mbps Ethernet =~ 50 mbps data transfer =~ 4.7 to 6.0 MB/s (max), and 1000 mbps Ethernet =~ 500 mbps data transfer =~ 47 to 60 MB/s (max) ]


How to tell if your system has USB 2.0 ports or USB 1.1 ports (Does my computer support USB 2 High Speed?)


Note: IEEE 1394b operates over CAT 5 twisted pair cable at up to 100 mbps, and over optical fiber from 200 mbps to 3,200 mbps (3.6 gbps or Gb/s). Data rates up to 1600 Mbps (S1600) are supported over shielded twisted pair cable over distances up to 4.5 meters. (In other words, FireWire over 2-pair CAT-5 cabling is limited to S100, but CAT 5E should allow up to 800 mbps.)

How fast is USB? Which is faster? How does this compare to other connections used with PCs and workstations?

      "High speed" USB 2.0 products have a design data rate (theoretical maximum) of 480.0  mbps. 
      "Full speed" USB  devices signal at                                             12.0  mbps, and
      "Low speed"  USB  devices   use a                                                1.5  mbps subchannel.
      serial port:                         115,000 bits per second                             0.115 mbps
      standard parallel port (Printer Port/Centronics interface):                              2.5  mbps max* 
           (*Enhanced Parallel Port (EPP)  ; for older "Bi-Directional", 150 kbps[kilobits per second])

      USB 1.1 ("Standard USB):     12 million bits per second (12 mbps) (approximately 1.5 MegaBytes/s) (aka 12  mbps aka 12Mb per second)
	   ECP parallel port:                          3   MillionBytes/s
	   IDE:                                   3.3-16.7 MillionBytes/s
	   SCSI-1:                                     5   MillionBytes/s
	   SCSI-2 (Fast SCSI, Fast Narrow SCSI):      10   MillionBytes/s 
	   Fast Wide SCSI (Wide SCSI):                20   MillionBytes/s

       Ultra-2 SCSI for a 16-bit bus:       up to 80   MillionBytes per second 
       FireWire (IEEE-1394):     100 to 400 mbps (12.5--50 MillionBytes/s)
       Ultra SCSI (SCSI-3, Fast-20, Ultra Narrow):     20 MillionBytes/s
       UltraIDE:                                       33 MillionBytes/s
       Wide Ultra SCSI (Fast Wide 20):                 40 MillionBytes/s
       Ultra2 SCSI:                                    40 MillionBytes/s
       Wide Ultra2 SCSI:                               80 MillionBytes/s
       Ultra3 SCSI:                                    80 MillionBytes/s
       Wide Ultra3 SCSI:                              160 MillionBytes/s
       FC-AL Fiber Channel:                       100-400 MillionBytes/s

Links and References:
- Ethernet Designations
- USB; from PC to External Hard Drive

in development: Update: (Nov 2007) "notes" (notepad) on eSATA vs. USB vs. Wireless (WLAN) Network

Real-World Tests:
1.Firewire; from PC to External Hard Drive

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[*2] Modifications: link to proposed new content added Nov 2007; Typo/error corrected March 2008.