a general sense, this term describes the information-carrying
capacity of a given transmission medium. It is a measurement of how much information
can be carried in a given time period (usually a second). It can apply to
analog telephone (POTS),
Ethernet networks, digital computer system buses,
signals, and VGA video signals used to connect projectors and
(the width of a band of electromagnetic frequencies) originally meant how much of the
electromagnetic frequency spectrum is allotted
for a given transmission path. Any
analog signal has
bandwidth is the width, or the range of frequencies, that an electronic
signal occupies. Bandwidth is literally the width of a band of
frequencies: one simply subtracts the lower limit (-3
of the frequencies used from the upper limit of the frequencies
used. Bandwidth is most commonly measured in cycles per second,
or hertz (Hz).
many cases for transmission over
twisted pair conductors or
optics it is often the same as the highest passed frequency (-3
dB point) because the low limit is assumed to be so close to zero
as to have no real effect. The higher this frequency, the wider
the bandwidth and therefore the greater the capacity of a
to carry information.
It should be
remembered that a real communications path usually consists of
a succession of links, each with its own bandwidth. If one of
these is much slower than the rest, it is said to be a bandwidth
In analog systems,
bandwidth is expressed in terms of the difference between the
highest-frequency signal component and the lowest-frequency signal
component. These frequencies are measured in the number of cycles
of change per second, or hertz therefore analog bandwidth is expressed
in hertz (Hz).
an example, consider the typical telephone (POTS) where the audio signals
are limited to the 300 to 3300 Hz range. A total of 3 kHz bandwidth
is required to transmit this signal. If we are sufficiently clever
we can manage to encode data onto this bandwidth with about 10
bps/Hz and get a modem to transmit data at 28.8 kbps.
An analog television
(TV) broadcast video signal is limited by the FCC to a bandwidth
of six megahertz (6 MHz) -- some 2,000 times as wide as a telephone
has over time acquired a general meaning of how much information
can be carried in a given time period (usually a second) over
a wired or wireless communications link. For example, a link with
a broad bandwidth - that is, a
broadband link - is one that may be able to
carry enough information to sustain the succession of images in
a video presentation (see Video Bandwidth).
In digital systems,
bandwidth is expressed as bits (of data) per second (bps). Thus, a
modem that works at 57,600 bps has twice the
bandwidth of a modem that works at 28,800 bps.
As a matter
of simplicity, we often do not attempt to make a distinction between
the two kinds of ways of measuring capacity and simply talk about
``bandwidth''. However, one must remember these are two very
different things: bandwidth sometimes refers to a measurement
of the range of frequencies used in an analog signal and sometimes
to the bits/second of digital data rate.
relates the bandwidth (analog bandwidth) to the data rate (digital
bandwidth) by stating that given a bandwidth of W, the highest
data rate is 2W. The data signal need not be encoded in binary,
but if it is, then the data capacity in bits per second (bps)
is twice the bandwidth in Hertz. Various manufactures use proprietary
signaling protocols to increase
this capacity by the transmitting more bits per data signal unit.
bad news about signaling is that the receiver must be able to
distinguish between the encoded data symbols in the presence of
outside interference, usually referred to as ``noise.'' Shannon's law
sets an upper limit on the bps/Hz ratio which increases logarithmically
with the signal-to-noise ratio. Theoretically, one should be able
to obtain between 2 and 12 bps/Hz, but current technology is blasting
past these theoretical limits.
example Bell labs recently announced there BLAST
technology. “BLAST is an extraordinarily bandwidth-efficient
approach to wireless communication which takes advantage of the
spatial dimension by transmitting and detecting a number of independent
co-channel data streams using multiple, essentially co-located,
central paradigm behind BLAST is the exploitation, rather than
the mitigation, of multipath effects in order to achieve very
high spectral efficiencies (bits/sec/Hz), significantly higher
than are possible when multipath is viewed as an adversary rather
than an ally.
our laboratory testbed, the BLAST team recently demonstrated what
we believe to be unprecedented wireless spectral efficiencies,
ranging from 20 - 40 bps/Hz. By comparison, the
efficiencies achieved using traditional wireless modulation techniques
range from around 1 - 5 bps/Hz (mobile cellular)
to around 10 - 12 bps/Hz (point-to-point fixed
microwave systems). In the 30 kHz bandwidth utilized by our research
testbed, the raw spectral efficiencies realized thus far in the
lab correspond to payload data rates ranging from roughly 0.5
Mb/s to 1 Mb/s. By contrast, the data rate achievable in this
bandwidth using typical traditional methods is only about 50 kb”
of Digital Bandwidth:
For modem users,
bandwidth is usually limited to 56 Kbit/sec, but depending on
various factors such as network congestion, it may fluctuate well
between 1Kbit/s and 50 Kbit/s. For higher speed connections such
as cable modem or DSL, bandwidth may easily go beyond 1 Mbit (1024
Kbit/sec). See the examples below for other examples of common
digital transmission protocols and there respective bandwidths:
T1, DS-1 - 1.544Mbps
E1, DS-1 - 2.048Mbps
T2, DS-2 - 6.312Mbps
E2 - 8.448Mbps
E3 - 34.368Mbps
T3 or DS3 - 44.736Mbps
OC-1, STS1 - 51.840Mbps
Fast Ethernet - 100.00 Mbps
OC-3, STS3 - 155.520Mbps
OC-3c - 155.520Mbps
OC-12, STS12 - 622.080Mbps
OC-48 - 2.488Gbps
OC-96 - 4.976Gbps
OC-192 - 10Gbps
OC-255 - 13.21Gbps
bandwidth refers to data-carrying capacity and is expressed in
cycles per second or Hertz (Hz). In the case of RAM, bandwidth
is a function of its rated speed and the size of its data path.
memory bandwidth statistic describes the amount of traffic, measured
in megabytes per second, that a computer system can move from
one level of memory to another.
Bandwidth is usually expressed in Bytes per Second.
Memory Bandwidth = (Memory Bus Width) x (Data Rate) x Number of
where Data Rate = (Memory Bus Speed x Operations/Clock Cycle)
order to calculate the bandwidth in Megabytes per seconds, the
bus speed must me divided by 8 to change bits to bytes.
bandwidth is 64 bits x 333MHz / 8, which equals about 2664MB/s
or aproximaly 2700MB/s, hence the reason that it is called PC2700.
In the case of RDRAM the formula is almost the same with the exception
that RAMBUS is only 16 bits. PC800's Bandwidth therefore would
be calculated as 16 bits x 800MHz / 8, which equals 1600MB/s.
We must now take into consideration that RDRAM supports dual
channel transfers; this doubles the effective bandwidth to 3200MB/s.
refers to a monitor's ability to refresh the screen. High bandwidths
allow more information to be painted across the display in a given
amount of time, which translates into support for higher resolutions
and higher refresh rates. Lower bandwidths result in flickering,
ringing artifacts, and ghosting.
the bandwidth of a monitor (measured in megahertz, or MHz), multiply
the horizontal resolution by the vertical resolution, and then
multiply the product of the two figures by the refresh rate. For
example, 1024x 728 x 75 = 56 MHz.
You may hear
bandwidth incorrectly used as the amount of time it takes a Web
page to fully load or as the amount of traffic on a Web site (this is also incorrect,
but widely used). HTML programmers often refer to larger graphics
as "bandwidth hogs" (because they take up
so much room and download so slowly).