In computer hardware, a port serves
as an interface between the computer and other computers or peripheral devices.
Computer ports have many uses, to connect a monitor, webcam, speakers, or other
peripheral devices. On the physical layer, a computer port is a specialized
outlet on a piece of equipment to which a plug or cable connects.
Electronically, the several conductors where the port and cable contacts
connect, provide a method to transfer signals between devices.
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| Physical Layer Port |
Physical Shape
Port connectors may be male or
female, but female connectors are much more common. Bent pins are easier to
replace on a cable than on a connector attached to a computer, so it was common
to use female connectors for the fixed side of an interface.
Computer ports in common use cover a
wide variety of shapes such as round (PS/2, etc.), rectangular (FireWire,
etc.), square (Telephone plug), trapezoidal (D-Sub — the old printer port was a
DB-25), etc. There is some standardization to physical properties and function.
For instance, most computers have a keyboard port (currently a Universal Serial
Bus USB-like outlet referred to as USB Port), into which the keyboard is
connected.
Electrical Signal Transfer
Electronically, hardware ports can
almost always be divided into two groups based on the signal transfer:
- Serial ports send and receive one bit at a time via a single wire pair (Ground and +/-).
- Parallel ports send multiple bits at the same time over several sets of wires.
After ports are connected, they
typically require handshaking, where transfer type, transfer rate, and other
necessary information is shared before data are sent.
Hot-swappable ports can be connected
while equipment is running. Almost all ports on personal computers are
hot-swappable.
Plug-and-play ports are designed so
that the connected devices automatically start handshaking as soon as the
hot-swapping is done. USB ports and FireWire ports are plug-and-play.
Auto-detect or auto-detection ports
are usually plug-and-play, but they offer another type of convenience. An
auto-detect port may automatically determine what kind of device has been
attached, but it also determines what purpose the port itself should have.
As of 2006, manufacturers have nearly
standardized colors associated with ports on personal computers, although there
are no guarantees. The following is a short list:
- Orange, purple, or grey: Keyboard PS/2
- Green: Mouse PS/2
- Blue or magenta: Parallel printer DB-25
- Amber: Serial DB-25 or DB-9
- Pastel pink: Microphone 1/8" stereo (TRS) minijack
- Pastel green: Speaker 1/8" stereo (TRS) minijack
Types of Port
1. Digital Visual Interface
Digital
Visual Interface (DVI) is a video display interface developed by the Digital
Display Working Group (DDWG). The digital interface is used to connect a video
source, such as a display controller to a display device, such as a computer
monitor. It was developed with the intention of creating an industry standard
for the transfer of digital video content.
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| Digital Visual Interface |
The interface is designed to transmit
uncompressed digital video and can be configured to support multiple modes such
as DVI-D (digital only), DVI-A (analog only), or DVI-I (digital and analog).
2. Display Port
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| Display Port |
The VESA specification is
royalty-free. VESA designed it to replace VGA, DVI, and FPD-Link. DisplayPort
is backward compatible with VGA and DVI through the use of adapter dongles.
DisplayPort is the first display
interface to rely on packetized data transmission, a form of digital
communication found in technologies including Ethernet, USB, and PCI Express.
It allows both internal and external display connections and, unlike legacy
standards where differential pairs are fixed to transmitting a clock signal
with each output, the DisplayPort protocol is based on small data packets known
as micro packets, which can embed the clock signal within the data stream,
allowing higher resolutions with fewer pins. The use of data packets also
allows DisplayPort to be extensible, meaning additional features can be added
over time without significant changes to the physical interface itself.
3. E-SATA
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| E-SATA |
- Minimum transmit amplitude increased: Range is 500–600 mV instead of 400–600 mV.
- Minimum receive amplitude decreased: Range is 240–600 mV instead of 325–600 mV.
- Maximum cable length increased to 2 metres (6.6 ft) (USB and FireWire allow longer distances.)
- The eSATA cable and connector is similar to the SATA 1.0a cable and connector, with these exceptions:
a. The eSATA connector is mechanically
different to prevent unshielded internal cables from being used externally. The
eSATA connector discards the "L"-shaped key and changes the position
and size of the guides.
b. The eSATA insertion depth is deeper:
6.6 mm instead of 5 mm. The contact positions are also changed.
c. The eSATA cable has an extra shield
to reduce EMI to FCC and CE requirements. Internal cables do not need the extra
shield to satisfy EMI requirements because they are inside a shielded case.
d. The eSATA connector uses metal
springs for shield contact and mechanical retention.
e. The eSATA connector has a design-life
of 5,000 matings; the ordinary SATA connector is only specified for 50.
4. IEEE 1394 Interface (FireWire)
IEEE
1394 is an interface standard for a serial bus for high-speed communications
and isochronous real-time data transfer. It was developed in the late 1980s and
early 1990s by Apple, who called it FireWire. The 1394 interface is comparable
to USB though USB has more market share. Apple first included FireWire in
some of its 1999 Macintosh models, and most Apple Macintosh computers
manufactured in the years 2000 - 2013 have included FireWire ports. However, as
of 2014, FireWire is being replaced by the Thunderbolt interface on most new
Macs. The 1394 interface is also known by the brand i.LINK (Sony), and Lynx
(Texas Instruments). IEEE 1394 replaced parallel SCSI in many applications,
because of lower implementation costs and a simplified, more adaptable cabling
system. The 1394 standard also defines a backplane interface, though this is
not as widely used.
.JPG) |
| IEEE 1394 Interface (FireWire) |
IEEE 1394 is the High-Definition
Audio-Video Network Alliance (HANA) standard connection interface for A/V
(audio/visual) component communication and control. FireWire is also available
in wireless, fiber optic, and coaxial versions using the isochronous protocols.
5. PS/2 Connector
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| PS/2 Connector |
6. Serial Port
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| Serial Port |
While such interfaces as Ethernet,
FireWire, and USB all send data as a serial stream, the term "serial
port" usually identifies hardware more or less compliant to the RS-232
standard, intended to interface with a modem or with a similar communication
device.
Modern computers without serial ports
may require serial-to-USB converters to allow compatibility with RS 232 serial
devices. Serial ports are still used in applications such as industrial
automation systems, scientific instruments, point of sale systems and some
industrial and consumer products. Server computers may use a serial port as a
control console for diagnostics. Network equipment (such as routers and
switches) often use serial console for configuration. Serial ports are still
used in these areas as they are simple, cheap and their console functions are
highly standardized and widespread. A serial port requires very little
supporting software from the host system.
7. USB
Universal Serial Bus (USB) is an
industry standard developed in the mid-1990s that defines the cables, connectors
and communications protocols used in a bus for connection, communication, and
power supply between computers and electronic devices.
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| USB |
USB was designed to standardize the
connection of computer peripherals (including keyboards, pointing devices, digital
cameras, printers, portable media players, disk drives and network adapters) to
personal computers, both to communicate and to supply electric power. It has
become commonplace on other devices, such as smartphones, PDAs and video game
consoles. USB has effectively replaced a variety of earlier interfaces, such
as serial and parallel ports, as well as separate power chargers for portable
devices.
8. VGA Connector
A Video Graphics Array
(VGA) connector is a three-row 15-pin DE-15 connector. The 15-pin VGA connector
is found on many video cards, computer monitors, and high definition television
sets. On laptop computers or other small devices, a mini-VGA port is sometimes
used in place of the full-sized VGA connector.
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| VGA Connector |
DE-15 is also conventionally called
RGB connector, D-sub 15, mini sub D15, mini D15, DB-15, HDB-15, HD-15 or HD15
(High Density, to distinguish it from the older and less flexible DE-9
connector used on some older VGA cards, which has the same shell size but only
two rows of pins).
VGA connectors and cables carry
analog component RGBHV (red, green, blue, horizontal sync, vertical sync) video
signals, and VESA Display Data Channel (VESA DDC) data. In the original version
of DE-15 pinout, one pin was keyed by plugging the female connector hole; this
prevented non-VGA 15 pin cables from being plugged into a VGA socket. Four pins
carried Monitor ID bits which were rarely used; VESA DDC redefined some of
these pins and replaced the key pin with +5 V DC power supply.
The VGA interface is not engineered
to be hotpluggable (so that the user can connect or disconnect the output
device while the host is running), although in practice this can be done and
usually does not cause damage to the hardware or other problems.
9. SCSI
Small Computer System Interface
(SCSI, /ˈskʌzi/ skuz-ee)[1] is a set of standards for physically connecting and
transferring data between computers and peripheral devices. The SCSI standards
define commands, protocols and electrical and optical interfaces. SCSI is most
commonly used for hard disks and tape drives, but it can connect a wide range
of other devices, including scanners and CD drives, although not all
controllers can handle all devices. The SCSI standard defines command sets for
specific peripheral device types; the presence of "unknown" as one of
these types means that in theory it can be used as an interface to almost any
device, but the standard is highly pragmatic and addressed toward commercial
requirements.
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| SCSI |
The SCSI protocol defines
communication from host to host, host to a peripheral device, peripheral device
to a peripheral device. However most peripheral devices are exclusively SCSI
targets, incapable of acting as SCSI initiators—unable to initiate SCSI
transactions themselves. Therefore peripheral-to-peripheral communications are
uncommon, but possible in most SCSI applications. The Symbios Logic 53C810 chip
is an example of a PCI host interface that can act as a SCSI target.
10. HDMI
HDMI (High-Definition
Multimedia Interface) is a proprietary audio/video interface for transferring
uncompressed video data and compressed or uncompressed digital audio data from
an HDMI-compliant source device, such as a display controller, to a compatible
computer monitor, video projector, digital television, or digital audio
device. HDMI is a digital replacement for existing analog video standards.
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| HDMI Connector |
Several versions of HDMI have been
developed and deployed since initial release of the technology but all use the
same cable and connector. Other than improved audio and video capacity,
performance, resolution and color spaces, newer versions have optional advanced
features such as 3D, Ethernet data connection, and CEC (Consumer Electronics
Control) extensions.
11. Phone Connector / Audio Connector
In
electronics, a phone connector is a common family of connector typically used
for analog signals, primarily audio. It is cylindrical in shape, typically with
two, three or four contacts. Three-contact versions are known as TRS
connectors, where T stands for "tip", R stands for "ring"
and S stands for "sleeve". Similarly, two- and four-contact versions
are called TS and TRRS connectors respectively.
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| Audio/Phone Connector |
The phone connector was invented for
use in telephone switchboards in the 19th century and is still widely used. In
its original configuration, the outside diameter of the "sleeve"
conductor is 1⁄4 inch (exactly 6.35 mm). The "mini" connector has a
diameter of 3.5 mm (approx. 1⁄8 inch) and the "sub-mini" connector
has a diameter of 2.5 mm (approx. 3⁄32 inch).
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