List of interface bit rates

Most of the listed rates are theoretical maximum throughput measures; in practice, the actual effective throughput is almost inevitably lower in proportion to the load from other devices (network/bus contention), physical or temporal distances, and other overhead in data link layer protocols etc. The maximum goodput (for example, the file transfer rate) may be even lower due to higher layer protocol overhead and data packet retransmissions caused by line noise or interference such as crosstalk, or lost packets in congested intermediate network nodes. All protocols lose something, and the more robust ones that deal resiliently with very many failure situations tend to lose more maximum throughput to get higher total long term rates.

Device interfaces where one bus transfers data via another will be limited to the throughput of the slowest interface, at best. For instance, SATA revision 3.0 (6 Gbit/s) controllers on one PCI Express 2.0 (5 Gbit/s) channel will be limited to the 5 Gbit/s rate and have to employ more channels to get around this problem. Early implementations of new protocols very often have this kind of problem. The physical phenomena on which the device relies (such as spinning platters in a hard drive) will also impose limits; for instance, no spinning platter shipping in 2009 saturates SATA revision 2.0 (3 Gbit/s), so moving from this 3 Gbit/s interface to USB 3.0 at 4.8 Gbit/s for one spinning drive will result in no increase in realized transfer rate.

Contention in a wireless or noisy spectrum, where the physical medium is entirely out of the control of those who specify the protocol, requires measures that also use up throughput. Wireless devices, BPL, and modems may produce a higher line rate or gross bit rate, due to error-correcting codes and other physical layer overhead. It is extremely common for throughput to be far less than half of theoretical maximum, though the more recent technologies (notably BPL) employ preemptive spectrum analysis to avoid this and so have much more potential to reach actual gigabit rates in practice than prior modems.

Another factor reducing throughput is deliberate policy decisions made by Internet service providers that are made for contractual, risk management, aggregation saturation, or marketing reasons. Examples are rate limiting, bandwidth throttling, and the assignment of IP addresses to groups. These practices tend to minimize the throughput available to every user, but maximize the number of users that can be supported on one backbone.

Furthermore, chips are often not available in order to implement the fastest rates. AMD, for instance, does not support the 32-bit HyperTransport interface on any CPU it has shipped as of the end of 2009. Additionally, WiMAX service providers in the US typically support only up to 4 Mbit/s as of the end of 2009.

Choosing service providers or interfaces based on theoretical maxima is unwise, especially for commercial needs. A good example is large scale data centers, which should be more concerned with price per port to support the interface, wattage and heat considerations, and total cost of the solution. Because some protocols such as SCSI and Ethernet now operate many orders of magnitude faster than when originally deployed, scalability of the interface is one major factor, as it prevents costly shifts to technologies that are not backward compatible. Underscoring this is the fact that these shifts often happen involuntarily or by surprise, especially when a vendor abandons support for a proprietary system.

By convention, bus and network data rates are denoted either in bits per second (bit/s) or bytes per second (B/s). In general, parallel interfaces are quoted in B/s and serial in bit/s. The more commonly used is shown below in bold type.

On devices like modems, bytes may be more than 8 bits long because they may be individually padded out with additional start and stop bits; the figures below will reflect this. Where channels use line codes (such as Ethernet, Serial ATA and PCI Express), quoted rates are for the decoded signal.

The figures below are simplex data rates, which may conflict with the duplex rates vendors sometimes use in promotional materials. Where two values are listed, the first value is the downstream rate and the second value is the upstream rate.

All quoted figures are in metric decimal units. Note that these aren't the traditional binary prefixes for memory size. These decimal prefixes have long been established in data communications. This occurred before 1998 when IEC and other organizations introduced new binary prefixes and attempted to standardize their use across all computing applications.

The figures below are grouped by network or bus type, then sorted within each group from lowest to highest bandwidth; gray shading indicates a lack of known implementations.

As stated above, all quoted bandwidths are for each direction. Therefore for duplex interfaces (capable of simultaneous transmission both ways), the stated values are simplex (one way) speeds, rather than total upstream+downstream.