Common plugs and connectors
(One of the ideas for this page is visual matching for things you are likely to find, another point is to show comparable connectors)
You may also be interested in
- 1 Multi-purpose, often home electronics, audio
- 2 Video cables/plugs
- 2.1 Composite video
- 2.2 Component video (YPbPr)
- 2.3 S-Video
- 2.4 SCART
- 2.5 VGA
- 2.6 Digital video cables (high speed and/or uncompressed)
- 2.7 D-Terminal
- 3 Computer
- 3.1 USB
- 3.2 8P8C / Ethernet cable
- 3.3 Molex power and Berg power connectors
- 3.4 PCIe, EPS, etc.
- 3.5 SATA
- 3.6 SAS
- 3.7 Firewire (IEEE 1394)
- 3.8 Thunderbolt
- 3.9 PS/2
- 3.10 D-sub (D-subminiature)
- 3.11 Ribbon-cable-and-IDC
- 3.12 Centronics connectors (Micro ribbon)
- 3.13 Fan connector
- 3.14 See also
- 4 RF/coax connectors
- 5 Power - device side
- 5.1 Low/medium voltage
- 5.1.1 DC connectors, EIAJ power, coaxial and more
- 5.1.2 3-Pin and 4-Pin DC Plugs
- 5.1.3 More specialized
- 5.2 Higher voltage (mains power)
- 5.1 Low/medium voltage
- 6 Power - wall plugs
- 7 Specialist
Multi-purpose, often home electronics, audio
TRS (Tip, Ring, Sleeve) and variations
Usually carries audio, occasionally basic signalling. The 3.5mm variation is also referred to as audio jack, mini-jack, jack plug, stereo plug, phone plug, and others.
Most commonly seen in the 3.5mm variant. You also see the 2.5mm variation, often for smaller devices, and the 6.35mm (1/4") connectors where sturdier connectors are useful.
The history of plugs like these is complex, and there are some leftovers today that use less usual variants.
But what you're most likely to meet is primarily:
- The 1/4", which is precisely 6.35mm
- US refers to it as 1/8" (0.125") though it's more like 0.138"
- best known for TRS in headphones for stereo sound for a few dozen years
- and TRRS for mic-and-headphones on smart phones
- US refers to it as 3/32" (0.09375") it's more like 0.098"
The latter two are standardized by millimeters, so the inches are approximations.
It seems they're always manufactured to mm sizes(verify) and if so, the difference is irrelevant as the inch figures are just easy names.
Also, the contact spring in the sockets that holds the plugs would make up small differences anyway.
See also 
- the sleeve is usually ground
- In headphone plugs, the tip, ring and sleeve are used for left, right, and ground, respectively.
- TS (Tip and Sleeve), e.g. for mono sound)
- TRS, stereo sound as above
- TRRS (Tip, Ring, Ring, Sleeve), e.g. in headphones with controller and/or microphone in the wire
- Android and Apple have standards. Different ones:
- Android uses OMTP (Left Right Mic Ground)
- Apple uses CTIA (Left Right Ground Mic)
- There are other variants, such as iPod's AV cable (Left Right Ground Video)
- (Also note Apple have a different (intentionally much harder to implement) remote system - see the next section
The buttons will be different resistor values between mic and ground pins.
0..70 ohm Function A, play/pause/takecall 110..180 ohm Function D, typically voice commands 210..290 ohm Function B, volume up 360..680 ohm Function C, volume down
(The impedance of the microphone itself is considerably higher, and sense-wise acts as the default)
~0 ohm is play/pause/takecall
Other things seem to be proprietary signaling, which allows them to add functionality over time. And piss of imitators and DIYers.
Used for audio, video (often composite, now also component), some simple data (like non-optical digital audio)
Named for its introduction by the Radio Corporation of America.
Other names include cinch connector, phono connector, and some odd ones out like the Dutch calling it a tulpstekker (after tulips).
DIN refers to a whole standardization body.
DIN connectors typically refer to a series of plug/socket system that have a 13.2mm-diameter round metal friction locking shield, which actually come from five different specific DIN standards. (It seems the original DIN standards are out of print, and you now want to read IEC 60130-9, which also expanded the series (verify))
The plugs were once more common. The main uses now are leftovers from older applications, including MIDI (and DIN sync), audio in+out on tape decks, the AT keyboard connector, some basic data signalling where a relatively sturdy connector was useful. (Note that many of these involve the 180-degree 5-pin plug)
Mini-DIN is a similar-looking variation also from DIN, with a 9.5mm round metal shield. Additionally uses plastic slots that makes plugging in plugs into wrong/different slots harder to do (it is easier to accidentally interchange some of the larger DIN plugs).
Probably mostly known for S-video (4-pin), and PS2 keyboard/mouse (6-pin variant). Other uses include audio, video, some fairly one-off video card adapters (see also Video), some communication Also applied in a number of proprietary uses - though those often see non-standard variants (see next section).
Nonstandard mini-DIN-like sockets and plugs
There are a number of non-standard connectors that have the same 9.5mm housing, but are not standardized or approved by DIN. These include:
Some of them are specifically designed to be compatible, some specifically incompatible with mini-DIN.
- DIN 41529: 2-pin, seen in loudspeakers
Modular connector (and Registered Jack); ?P?C
(Note: 'Registered Jack' refers more specifically to telephone wiring using these jacks)
Variations are named by how
- many positions there are in the plug (which also implies the plug's width), and
- how many conductors are actually present in this particular plug (filled out from the center positions).
For example, 6P2C has 6 positions and two conductors, 8P8C has 8 positions and has conductors in all positions.
The 2, 4, 6, 8 positions/lead connectors are mostly standard, 10P10C also exists.
Some commonly seen variations/applications include:
- Ethernet cables (100BASE-TX, 1000BASE-T) use 8P8C connectors. These plugs are also seen in telephone wiring, commonly in companies, and more widely in a few countries
- Telephone plug is often a 6P2C or 6P4C plug plugging into a 6P socket (6P6C, 6P4C and 6P2C are all seen in different contexts)
- It is not unusual to see 4P4C to connect phone handset to the phone body
One of the potentially useful things about these plugs is that smaller plugs fit in larger sockets, e.g. 4P and 6P plugs fit in 8P sockets.
Since the clip centers the plug, and some wiring standards consider related wiring standards, plugging thing into (larger) sockets occasionally makes sense. For example, you could wire 8P8C sockets in a building to carry both phone wiring (middle two pins) and 100Mbit networking (since 100BASE-TX only does not use the two center pins that 6P2C type phone connections use - it uses two of the other pairs)
The plugs are somewhat associated with applications/wirings - some to the point that some people use them synonymously - but that only makes sense in specific contexts. Some of the more common ones (For larger lists, see e.g. [Wikipedia: Registered_jack#List_of_official_types] ):
- 4P4C ~ RJ9 (mostly used to connect handsets to phones - two pairs, one for the microphone and one for the speaker)
- 6P2C ~ RJ11 (one-pair, one telephone line)
- 6P4C ~ RJ14 (two-pair, two telephone lines)
- 6P6C ~ RJ25 (three-pair, three telephone lines)
- 8P8C ~ RJ45 (sort of; see below), and RJ49 (ISDN)(verify)
The standard called RJ45 is obsolete (and historically associated with 8P2C). People who say RJ45 are usually thinking of 8P8C plugs wired according to TIA/EIA-568-B (for Fast Ethernet) (not 8P2C wired according to RJ45).
Note that not all RJ standards use this plug type; see e.g. RJ21
- http://en.wikipedia.org/wiki/Registered_jack (telephone wiring)
While TOSLINK specifies a few plugs, it is mostly associated with the optical EIAJ/JEITA RC-5720 plug, a.k.a. JIS F05 and CP-1201 - optical, with a square-ish shape on the end.
In most contexts, this plug carries S/PDIF protocol (which itself can carry PCM, DTS/DCA, and AC3). (S/PDIF can also be carried over copper, often connected via RCA or BNC).
Mini-TOSLINK looks like a stereo jack (3.5mm TRS style) but carries fiber to its tip.
There are physical adapters from mini-TOSLINK to TOSLINK.
This allows laptops (and other size-restrained devices) to have one small socket that provides both a stereo jack, and digital audio connector.
The 4mm version often carries lowish-current power or occasionally audio (amp/speaker connections), and is seen for for measuring devices, such as multimeters (and e.g. banana-to-BNC for oscillosocopes).
The banana plug is named for the curve that comes from the lengthwise springs that friction-lock the plug. Actually, shapes vary, and not all 4mm plugs have a friction-lock design, but most do.
There is a 2mm plug sometimes seen in similar situations, but it was never used as widely - and it is not often referred to as a (variation of) banana plug, because the lengthwise springs are not there.
|This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)|
Carries Y, U, and V with sync pulses, and is also easy to broadcast - it is almost entirely the same as analog TV's format. Video recorders and some early computers modulate such a signal onto a local video channel, on their antenna output wire.
The main upsides to composite is probably that it is easy to transfer video between devices with a simple, common plug.
The main downside is that it susceptible to various visual artifacts, including noise/interference, dot crawl, also depending on the quality of the encoding/decoding hardware.
Quality you get from composite video varies noticeably between different (types/qualities/designs of) devices, and you want to use only shortish cables.
Composite video can also be called CVBS, an acronym with various possible readings, depending on who you ask: "Color, Video, Blank and Sync", "Composite Video Baseband Signal", "Composite Video Burst Signal", or "Composite Video with Burst and Sync".
Component video (YPbPr)
More broadly, it can refer to any system that sends video in multiple separated channels.
While the plugs used for YPbPr components are red, green, and blue, this is not RGB video (which also exists, in multiple forms, and they could all be called component video.
(Green plug carries the Y signal (Luma), the blue the Pb (blue minus yellow), and the red the Pr (red minus yellow) signal)
S-Video (also Super Video or Separated Video, and also sometimes called Y/C) carries luma (Y) and chroma (C) signals on separate wire pairs, using standard 4-pin mini-DIN plugs.
It is similar to composite video in that it carries the same information, but avoids joining and having to separate the Y and C information, and avoids some cheap, low-quality implementations that exists in composite video (the modulation and demodulation of the Y and C channels). Still, in fairly ideal conditions (for composite), S-Video is no better than composite.
S-Video-to-Composite-video converter cables can just join the wires (although this may mean the colors are less saturated - something about the voltage amplitudes of these two signals?(verify)). Note that you can not use that same converter to go from composite to S-Video, as that would put a mixed Y+C channel on both the Y and C pairs. The S-video decoder hardware will usually partially understand this, which results in a black and white image(verify).
You may find video-related cables that resemble the 4-pin mini-DIN S-Video plug. This includes:
- Video cards may come with a 7-pin plug. This is rarely a standard mini-DIN plug, and often has its plastic slot in the same place as on the 4-pin DIN plug, but wider, so that the video card socket will accept a standard S-Video plug, and also the plug on the cable supplied with the card which uses the extra pins to carry, usually, another type of video (often composite video, sometimes composite video).
- and 9-pin variation called VIVO, also seen on video cards, that allows S-Video in, S-Video out, component out, and composite out.
- a different 7-pin connector (standard mini-DIN) used on some professional (VCR) kits
SCART (also Euro AV, EIA Multiport) combines formats used by various common plugs, making it somewhat easier to connect various common home devices. Before HDMI, SCART was very common on VCRs, TVs, and also frequently seen on DVD players and such.
SCART can carry:
- Mono/Stereo Audio, both ways
- Composite video, both ways
- S-Video may be supported both ways, but isn't always implemented
- RGB (on newer hardware, by re-purposing some wires, so both ends need to support this (ab)use)
You can find plugs that convert to composite, audio, and S-Video, and sometimes versions with a switch that selects whether you want to use the converter plug to do input or output.
RGB is higher quality, but
- has to be supported by both sides
- can also not be used at the same time as S-Video output
- is only meant for player-to-display travel.
Supported primarily by some more modern TV sets (receiving role) and recent media players (sending role) although supporting players only use RGB when you explicitly configure them for it, for compatibility reasons.
- EN 50049-1
Computer video is digital in memory, and converted to analog for transmission.
It' now typically converted back to digital for display which, yes, is a weird situation and asking for signal losses. It makes but sense for historical reasons but is also the reason we're now moving to digital transmission.
Digital video cables (high speed and/or uncompressed)
|This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)|
On digital and/or analog
DVI can carry both analog and digital video, but specific wires and interfaces can choose to do just one.
In the plugs, there is a plate on one side - if there are pins around that (red in the pinout image on the right), the cable can carry analog video.
If there are pins around the plate, it can carry analog video.
If the block of pins close to it is not a full 3x3 block, the cable can carry only analog and is called DVI-A.
If there are at least two blocks of 3x3 pins, the cable can carry digital video.
If it can carry only digital and not analog (no pins around the plate) it is called DVI-D.
If it is one solid block of pins (that is, includes the blue pins in the image on the right), it can do dual-link digital.
If it can carry both digital and analog (3x3 block and pins around the plate) it is called DVI-I.
There are some other connectors that look like DVI, such as:
- VESA P&D / M1-DA (an extension to DVI from VESA)
And two different many-pin connectors, often seen for many-monitor graphics cards, as each connector can be used for two monitors:
Needs an adapter for things like DVI or VGA (doesn't carry them directly). The absence of pin 58 in DMS-59 seems to be just for keying. It isn't used in LFH either(verify), so you can use DMS-59 cables where you would otherwise use LFH.(verify)
MiniVGA, MiniDVI, MicroDVI, Mini DisplayPort
- mainly in Apple hardware (mostly MacBooks), not standardized.
- replaced by Mini DVI (which could also go to VGA) and MiniDisplayPort (which does even more)
- mainly in Apple hardware (mostly MacBooks), not standardized
MicroDVI, again mostly Apple, was used on some Macbook Airs. There are adapters to VGA and to DVI-D (not DVI-A / DVI-I). Looks somewhat like an USB port. It was discontinued in favour of Mini DisplayPort
- Initially in Apple laptops, now adopted by VESA and starting to be used by other vendors
- There are converters to VGA, (Dual-Link) DVI, HDMI, Displayport, and probably more
Other Apple connectors
Intel and Apple developed Thunderbolt, which uses the same plug as Mini DisplayPort.
This is intentionally backwards compatible though also potentially confusing, because e.g. the same Apple monitor will do more on one laptop than another.
It's safe to connect, but any feature beyond displaying won't work.
You can tell by the logo:
- monitor-like logo → Mini DP
- lightningbolt logo → Thunderbolt.
Note that Thunderbolt 3 uses the standardized USB-C (which is now entering general use), so mini-DP-style thunderbolt is now sometimes referred to as Thunderbolt 2 connector.
Thunderbolt is, by name and perhaps logo, easy to confuse with Lightning.
Lightning is the thin flat reversible plug with little strips of connector. It is almost exclusive to iPhone, iPad, iPod, and a handful of Apple accessories. It can do charging, USB data connection, video out, audio out, and apparently SD card reading(verify)
High-Definition Multimedia Interface (HDMI) 
Digital transfer. Can carry HD video, and audio. Has hardware-level copy protection (HDCP).
There are plug variants.
- Type A is by far the most common, what you usually use
- Type B has more data lines, designed for very-high-bandwidth applications, but never got used. DisplayPort now make more sense in practice
- Type C is the mini variant (meant for small/mobile devices)
- Type D is the micro variant (meant for small/mobile devices)
- Type E is an automotive variant - locks in place, more resistant to moisture and dirt
- you can also get type A in a harness, giving similar features
(For computers it can be relevant that HDMI can carry DVI-D fairly directly - though this will probably only work if the DVI device supports HDCP, because the HDMI side is likely to require it)
CEC (Consumer Electronics Control) is for simple commands between a set of interconnected devices, e.g. allowing your TV remote to control some common functions of a set-top or DVD player, have a device turn the TV on and to it as a source, control volume, transfer a preferred device name, things like that.
It's mostly known under other, nicer sounding names, like Anynet+ (Samsung), 1-Touch Play (Roku), something involving Link (lots of brands),
Electrically it is a one-wire bidirectional serial bus, separate from HDMI communication so that that can sleep, and very slow
Specs say 2 or 3 meter max. This is a cautious figure and decent cable quality may go a little longer, yet don't count on more than 10-20m, and usually only for lower(-data-rate) resolutions.
Active cables could go up to 15-30m at somewhat higher rates/resolutions and a more standard-compliant way. These must be connected in the right direction (passive cables don't care).
If you want more than that, you probably want fiber DP instead of copper (at high enough rates and distances, the issue is capacitance and sort of unavoidable).
A Dual-mode DisplayPort (a.k.a. DP++) output supports the use of an adapter to single-link DVI or HDMI. (a passive adapter in that the output itself already speaks the right thing, the adapter only changes voltages)
Without this, only an active adapter (something that does a conversion between different video formats inside it) would work. Other formats (e.g. VGA) always require this.
A single lane (differential pair) in a DP cable can be run at one of four speeds,
- 1.6GBit/s raw, ~1.3GBit/s data in RBR (reduced bit rate)
- 2.7GBit/s raw, ~2.1GBit/s data in HBR mode
- 5.4GBit/s raw, ~4.3GBit/s data in HBR2 mode (introduced in DPv1.2)
- 8.1GBit/s raw, ~6.5Gbit/s data in HBR3 mode (introduced in DPv1.3)
Cables made for higher speeds will often be 4-pair, which means:
- 4-pair HBR is ~8 Gbit/s (~10 raw minus 20% coding overhead)
- 4-pair HBR2 is ~17 Gbit/s (~21 raw minus 20% coding overhead)
- 4-pair HBR3 is ~25 Gbit/s (~32 raw minus 20% coding overhead)
Your average monitor will just work - e.g. making 1920×1080 not work is roughly impossible on a short cable. These numbers are useful if some combination of 4K, deep color, 120fps, and/or 3D is your thing. e.g.
- 3840×2160@120fps requires HBR2,
- 5120x2880@60Hz require HBR3
- multiple displays on a single port can be done
Seen used on laptops in general, and Apples in general, for monitors
Also used on Apples for Thunderbolt (1 and 2)
Gigabit Video Interface (GVIF), carried by a single twisted pair of wires
Apparently deprecated in favour of DisplayPort(verify)
D-Terminal (not to be confused with D-Subminiature (a.k.a. D-Sub)), probably most common in Japan, and seen elsewhere in specific applications, e.g. digital satellite tuners.
The wires carry component video, and signal lines that use logic-level voltages to signal the current video's resolution, ratio, and whether it is interlace/progressive.
Can carry HD resolutions
Breakout cables to component video over RCA and BNC exist.(verify)
|This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)|
From most to least common (well, a guess at that):
- USB A: The plug/socket seen on the computer side and USB hubs (and sometimes elsewhere, e.g. on printers for direct camera connection)
- USB B: Used on the device side for bulkier devices, such as scanners and printers, where there are no space limitations, and sturdiness is handy
- USB-C: Invertible. Seen on smartphone, some apple products. (released ~2014.
- Developed parallel to USB3, and as of this writing the two don't support all the same features (verify)
- USB mini-B: Used by various smaller devices, such as cameras, MP3 players, some phones
- USB micro-B plugs and sockets, meant for use in thinner devices. example: smartphones data/charge cables.
- USB3 A: Plug adds the extra lines for USB3, but remains the same size. Socket can take earlier (USB1, USB2) USB A.
- USB3 B: Plug adds the extra lines for USB3, and is bigger. Socket can take earlier USB B.(verify)
- USB3 micro-B - basically USB2 alongside USB3(verify), separated with a notch. Seen e.g. on 2.5" external hard drives, USB3 hubs.
- USB3 Micro-A (looks like USB3 micro-B but squarer) exists only as ap lug, and seems rare
- USB3 Micro-AB (looks like USB3 micro-B but squarer) refers to a socket that takes USB3 Micro-A and USB3 Micro-B, also seems fairly rare
- USB mini-AB socket socket (only), relatively rare, can accept both Mini-A and Mini-B plugs.
- USB micro-AB socket socket (only) that can accept both Micro-A and Micro-B. Defined by USB On The Go (OTG) (2001 standard)
- USB micro-A plugs and sockets, meant for use in thinner devices
- USB mini-A: was never seen that much, perhaps because it is confusable with mini-B.
- There are a number of non-standard plugs and sockets that are used to communicate USB, such as an 8-pin mini-sized plug, with 5 USB pins, and the other 3 pins regularly missing (usable for audio+video on some cameras). This plug is sometimes confusingly called B(-type).
- USB3 sockets and plugs (particularly on the computer side) are often indicated with either blue plastic, or SS (for Super Speed, the mode that USB3 adds)
- micro plugs/sockets are often not blue, possibly because it would be hard to see anyway(verify)), and because they're less ambiguous that PC-side A sockets
- The USB1/2 mini connectors are approximately 3mm by 7mm, the micro versions are mostly thinner, making them useful on very slim devices like smartphones.
- various game consoles based their controller communication on USB for a while, but with their own connectors (Which exactly?(verify))
8P8C / Ethernet cable
For the series of connectors, see #Modular_connector_.28and_Registered_Jack.29.3B_.3FP.3FC
For the use of 8P8C in ethernet, see Network wiring notes - 8P8C / RJ45
Molex power and Berg power connectors
Molex plugs in computers usually refers specifically to Molex 8981 (Molex in general being a company that makes many types of plugs), and is seen mostly on computer power supplies for HDD and CD drive connections CD/DVD drives and the likes.
It was standard for many years, though has now been largely displaced by SATA power plugs.
The other common Molex plug in computers is Mini-Fit Jr., used for PSU-to-motherboard connectors and the extra direct 4 and 6 pin (video card, CPU) power input.
The Berg plug is also named after its designer (though this is also (probably mistakenly?) called 4-pin mini-Molex). The Berg plug is the smaller plug used on 3.5 inch floppy drives. These plugs are becoming about as rare as those floppy drives themselves.
PCIe, EPS, etc.
- Two +12V, officially
- Three +12V, unofficially (Most cables/PSUs allow real current, even though the last pair is specced as NC)
PCIe 8-pin - an expansion of the 6-pin
- Three +12V
- with the pin that the 6-pin variant listed as NC used for +12V
- The extra two pins may be separated to be compatible with the 6-pin variant
- the extra 2 add Gnd and Sense
4-pin ATX 12V
- two +12V, two ground
- used for power more directly to the CPU, has been around since roughly the pentium 4
EPS12V, also known as '8-pin ATX 12V'
- four pairs of +12V and Gnd
- physically incompatible with PCIe 8-pin
- mostly seen on server boards
- refers to plug only: splittable, so that a PSU can accomodate motherboard with either the 4-pin or 8-pin CPU connectors (ATX 12V, EPS 12V)
- unrelated to GPUs, they use the PCIe ones. (For the 8-pin plug you can typically tell the difference: three yellow lines (PCIe) or four (ATX/EPS))
There are more variants, but most of us care only about the 7-pin data cable and the 15-pin power cable.
To avoid breaking the plastic of the motherboard data socket, a variation was introduced with more holder plastic around it. To avoid accidental removal, a clip was added that can be used in them (see images on the right).
For external use there is eSATA, which is pin-compatible, but the connector and socket are a little different, mostly for plugging safety (and so that you can't plug SATA cables meant for internal use onto external ports).
There is also eSATAp (often marked eSATA+), which is a connector that adds power, and the ability to plug in USB into this same socket. Keep in mind that this may be USB2 or USB3 (you can usually tell by the color).
Only the 5V line is guaranteed on the plug, the 12V line is optional. Desktop computers provide 12V, laptops usually don't.
This means eSATAp sockets can always power 2.5" drives (which only need +5V), but only the desktop variants can power external 3.5" drives (which also need 12V).
eSATApd unofficially (and therefore only sometimes) refers to having both voltages.
Basic SATA's basic power connector has so many pins for scalability reasons - it provides three voltages (3.3V, 5V, 12V), with three pins each to be able to meet requirements of power hungry drives (while not exceepding 1.5A per wire), plus one signalling cable.
This cabling is often not necessary, and there are slimline and micro versions of the power connector, which use simpler wiring, and are good enough for the drives they're meant for.
- if the SATA connector comes from a Molex plug adapter, you cannot hot-plug/swap the power (verify)
- the 3.3V line is currently often unused
SAS and SATA were designed compatibility in mind.
SAS (Serial Attached SCSI) is the fancier Enterprise-style variant of SATA. SAS adds a bunch more options, cables with more channels to attach more drives e.g. to RAID cards, internally and externally, and other such options.
The SAS and SATA drive connections are closely related, and in fact pin-compatible. You can physically plug SATA drives onto SAS controllers, the SAS drive connector (SFF-8482) allows it.
While SAS can tunnel SATA, the opposite is not true, and for this reason, you cannot use SATA cabling on a SAS drive (physically, because of the extra plastic). While you can find adapter to do this (they exist), the SAS controller may well assume full SAS behaviour(verify).
- Beyond single drives
Firewire (IEEE 1394)
IEEE 1394 is better known as FireWire (Apple), and sometimes i.LINK (Sony), and Lynx (Texas Instruments).
It was meant as a successor to parallel SCSI, and is also commonly used for some digital cameras, and for high-end audio and video devices. Was a potential competitor to USB in many areas, but while USB is somewhat slower (depending on which variant of FireWire and USB), USB is more popular for many things.
- smaller, e.g. used on more portable devices like cameras. Data-compatible with the 6-lead connector, but doesn't provide power. Initially developed by Sony, later more widely adopted(verify)
- two twisted pairs of data
- 6-lead ('alpha')
- two twisted pairs of data, power
- 9-lead ('beta')
- two twisted pairs of data, power, shield (verify)
- 8P8C connector (used in 1394c)
- IEEE 1394, specifically IEEE 1394-1995
- IEEE 1394a, specifically IEEE 1394a-2000, also known as FireWire 400
- Uses the 4-lead and 6-lead ('alpha') connectors
- IEEE 1394b, specifically IEEE 1394b-2002, also known as FireWire 800 (Apple's name)
- adds the 9-lead ('beta') connector
- IEEE 1394c, specifically IEEE 1394c-2006, also known as FireWire S800T
- adds the 8P8C connector
Fast peripheral interconnect by Intel and Apple. (Developed by Intel under the name Light Peak, since renamed)
Assume ~3 meter max over copper.
Can daisy-chain a few devices (though individual devices have to have the plugs and allow it)(verify).
Thunderbolt 1 reuses the Mini DisplayPort connector; thunderbolt capability is indicated by a lightning symbol.
- Can carry DisplayPort, one or more PCI Express lanes, and up to 10W of power.
- Copper cables carry two 10GBbps (1.2GByte/s) lanes, of which any device can use only one (seems a fair-sharing thing)
- Much like 1. Largest difference seems to be that devices can use both channels
Thunderbolt 3 uses USB-C connectors. Plugs and sockets should bear the thunderbolt logo.
- Speaks more protocols (DisplayPort, PCIe, USB 3, ...)
- Allows adapters to the previous MiniDP plug
- Not guaranteed to carry 10W as before (though USB could choose to do more than that)
- Assume it can do 20Gbps as before. Short or active cables could do 40Gbps(verify)
On Thunderbolt 3, USB3, and USB-C
It is intentionally protocol-agnostic.
- this makes adapters to HDMI, DP, earlier Thunderbolt, and earlier USB easier
- this allows other protocols to use the cable, which is what Thunderbolt 3 is doing.
- Protocols commonly seen include:
- USB3.1 (5 or 10GBps)
- USB2 (0.48GBps)
- Thunderbolt 3 (10GBps)
- USB Power Delivery
- just video (DisplayPort, HDMI, MHL)
- ...or some combination.
- Which ones a it does is context-dependent.
Thunderbolt 3 chose USB-C plugs/cable (previous versions used mini-DisplayPort), and TB3 can in many contexts be seen as an extension of USB3.
Note that for that reason, a Thunderbolt3 device will do nothing on a USB3-only host.
(sort of similar to how an earlier mini-DisplayPort monitor-only output will not speak earlier Thunderbolt, even though they adopted the same connector)
Ideally the difference should be simple to understand, but time will tell.
There in general a bunch of backwards compatibility and cross-compatibility, yet exact feature set varies, particularly as of this writing.
(Also not all USB-C is USB 3, but that should be irrelevant in practice)
Depending on adoption, the worst that can happen is either
- that things will work everywhere but not always at the same speed (who cares)
- or that some things will plug in but not work because it's vendor-specific (BLAH)
USB-C cables are created roughly equally in theory
- in that USB-C-to-USB-C should support everything that connects that way
- because it's protocol-agnostic
- and everything else is an active adapter that translates to whatever it's connecting
- but this isn't always as universal as you'd like
- not all cables support the same speed
- it may be capable of sustaining 40Gbit, 20Gbit, 10Gbit, 5GBit, or even just 480Mbit
- and which of the standards (TB3, DP, USB3, USB2) and which of their modes, will vary
- not all cables support charging (verify)
- and if they pretend to do so, but are out-of-spec knockoff cables, this is riskier now because there's more current involved than in earlier USB
Uses the 6-pin mini-DIN connector. For keyboards, this replaced the larger DIN plug used on AT style computers before PS/2. For mice, this became an alternative to serial port mice, though USB is now also quite common for keyboards and mice.
Most D-subminiature plugs have two rows of pins (some three), and a shell for seating and earthing.
Some common examples:
- DE-9: often a serial port (RS232) interface
- DB-25: Parallel ports (also once for serial ports), sometimes (older) SCSI
- DE-15: VGA monitor connectors. (Uses three rows of pins. Also technically called HD-15, where HD stands for the High Density of the pins compared to other D-Sub plugs)
- DA-15: Often seen on sound cards, originally for joysticks, later mostly for MIDI cables
The letter is the shell size, the number the amount of pins present.
Optionally there's a F or M on the end for female or male.
(which mattes mostly when mentioning a specific side of a specific type of use. For example, the parallel port on the back of a computer is DB25F, the serial port DE9M).
The shell size will usually softly imply to how many pins the variation could house, though it's not a 1-to-1 relation.
Also, how many it could house is not always how many it actually does house. Consider for example DB13W3 (and also a few incorrect references, or unusual variations).
Some have used specific letter codes thinking that they referred to the D-sub plugs in general, and started patterns of misleading use for those that do know what they mean.
- http://en.wikipedia.org/wiki/DB13W3 ('Sun video', or SGI/DCC)
In computer circles mostly known as ribbon cable, not naming the plug. (The plug is called an insulation-displacement connector, IDC (also DIN 41 651)).
The IDC pitch (hole spacing) is often 2.54mm (0.1 inch), though there are variations. For example, notebook parallel ATA connectors have 2.0mm pitch.
Common variations in computers:
- 40 pin, 2.54mm pitch - 3.5" hard drive connectors (parallel ATA)
- 44-pin, 2.0mm pitch - 2.5" notebook hard drive connectors (parallel ATA)
- 34-pin, 2.54mm pitch - floppy connectors (controller side, and drive side for 3.5" floppy drives)
- Some motherboard-connected back ports not directly soldered to the motherboard, e.g. an extra serial port, midi/gameport, USB ports (varying pin details), audio connectors (varying pin details).
Beyond that it's used internally in a lot of places.
Centronics connectors (Micro ribbon)
Perhaps best known for use in
- 36-pin: IEEE 1284 printer cables, specifically a male DB25 plug to male 36-pin Centronics plug (this use is mostly outdated)
- 50-pin: SCSI-1 (also mostly outdated)
PC fans are often connected with a three-pin connector (polarized variant from the Molex KK family) which supplies 12V, ground, and a sensor wire that the computer can use to count revolutions.
There were a few not-so-standard variation, such as Dell's.
You now commonly see Intel's variation, with a fourth pin to the side.
- 1 - Ground (black)
- 2 - 12V (often red)
- 3 - Fan Tach In (often yellow)
- 4 - PWM signal - seems to be a TTL signal that the fan uses via a transistor(verify)
6-pin (seen in servers) add:
- 5 - fan presence (lets the computer do a simple test to see there is one connected)
- 6 - fan fault led (for visual feedback which one is broken, useful in datacenters)
In other words, you can always plug in a fewer-pin fan. As long as you know which one is pin 1.
- some motherboards can vary voltage on the 12V pin. Some can do both this and PWM.
- using PWM fans is still the preferred method, because PWM'd 12V will manage to still spin at lower speeds than voltage regulation (for an interesting combination of reasons)
- 3-pin fan on 4-pin header is fine, will run at full speed
- because they don't even know about the PWM pin
- most 4-pin fans are designed to work fine on a 3-pin header
- (and will run at full speed)
If you have 3-pin fans and still want speed control:
- you can undervolt a fan with a ghetto-ish fix: splice a fan between the +12V and +5V (e.g. from a molex plug) giving 7V.
- However, not all fans spin up reliable at 7V, so check that it does or you'll have no cooling at all.
- there are little boxes you plug between motherboard and fan.
- which typically regulate the 12V line to lower (using filtered PWM).
- with a little soldering you can make a 3-pin fan PWM capable.
- (transistor and resistor, optionally a diode)
- Buuut 4-pin fans are not that expensive, so this is generally not worth it
Plugs desiged (mostly in terms of shielding and impedance) to carry radio frequencies, associated with carrying video, data, and more.
Belling-Lee (IEC 169-2)
Used for TV (and radio) connectors in some european countries.
Diameter is ~9mm(verify)
Some people seem to call this a PAL connector, probably through association. Some call it a coax plug, which is even vaguer.
Note that on houses with more serious installations, it's not unusual to see these only in the eventual wall-plug and the cable that goes to the TV, and e.g. F collectors on signal boosters and such. This because the Belling-Lee plugs are not ideal for VHF and UHF frequencies (but fine for MW and Shortwave).
F Connector (IEC 169-24)
Often used for cable television / cable modems, satellite television, and (American) TV aerial connections. A little better for VHF and UHF than Belling-Lee is.
BNC, Bayonet Neill-Concelman (also sometimes Baby Neill-Concelman connector, Baby N connector, British naval connector, bayonet nut connector) was once common for networking. Still used for some antennae, video (then often composite video), occasionally audio and other things.
TNC, Threaded Neill-Concelman, is a variation on BNC with a screw thread system (BNC uses bayonet).
Reverse TNC is reverse in that the inward/outward threading is switched between male and female plugs. This is seen e.g. in WiFi antennas, an area where R-SMA is also regularly seen(verify).
The Type C Connector looks like BNC, but is bigger.
(BNC was developed as a smaller version of this )
SMA and reverse SMA
Diameter: ~6mm for the thread/female, ~8mm for the male/outside
SMA is short for for SubMiniature version A. There are also SMB and SMC connectors.
A variation on SMA called RP-SMA ('reverse polarity') is used in WiFi antenna connectors (R-TNC also sees use there).
Diameter: ~4mm for the thread/female
U.FL / MHF / I-PEX / IPAX / IPX / AMC / UMCC
These various names all tiny connectors for high-frequency RF signals, and mostly interchangeable. Seen in various mobile and wireless applications.
There are adapters to things like (RP-)SMA sold for applications such as WiFi, mobile modules (particularly M2M), and others.
Unsorted RF connectors
Power - device side
...e.g. adapters, battery packs, solar panels, and such.
Meaning up to a dozen volts, generally up to an amp or two.
DC connectors, EIAJ power, coaxial and more
Usually used for low-voltage power, most under 20V, and (so) typically used for DC.
Up to a few millimeters thick, often either concentric barrel-style or tip-(ring-)sleeve style.
Most are not so much standardized as they are used by convention, and consistently produced. There are enough variants htat it can can be hard to recognize even some more standard ones with certainty.
There are perhaps half a dozen common plugs/sockets, and probably at least a dozen or two more variants.
In the image on the right, from top to bottom:
- 2.5mm TS (somewhat confusable with audio)
- 3.5mm TS (confusable with audio)
- 5.0mm barrel (~6.2mm tip) (verify)
- EIAJ-01 (2.35mm barrel, 0.7mm inner diameter)
- 3.5mm barrel (1.35mm(verify) inner diameter)
- EIAJ-02 (4.0mm barrel, 1.7mm inner diameter)
- 5.5mm barrel, for 1.5mm pin
- 5.5mm barrel, for 2.5mm pin
Terms, standards, plugs:
- IEC 60130-10 (:1971) defines five/seven connectors
- Type A: 5.5 mm outer diameter, 2.1 mm inner diameter (seems the most common?)
- Type A: 5.5 mm outer diameter, 2.5 mm inner diameter
- Type B: 6.0 mm outer diameter, 2.1 mm inner diameter
- Type B: 6.0 mm outer diameter, 2.5 mm inner diameter
- Type C: 3.8 mm outer diameter, 1.4 mm inner diameter
- Type D: 6.3 mm outer diameter, 3.1 mm inner diameter
- Type E: 3.4 mm outer diameter, 1.3 mm inner diameter
- EIAJ RC-5320A  defines five different thicknesses of barrel pairs rated for 2A:
- 'EIAJ connector' usually refers to one of the connectors. ()
- Yellow-tipped DC connectors are likely to be one of these
- EIAJ RC5322
- Barrel type connectors, 6mm outer, 3.1mm inner radius. Pin is 1.0mm
- wide (6.5mm) plastic tip, apparently to avoid contact in cars and such
- EIAJ RC-5322
Telling which one you have or need is sometimes be a bit of a challenge. Small mismatches on the slightly-smaller side tend to be okay, because these are often held by spring contacts.
For example, my big boxs o' 5V and 12V wallwarts, of the barrel connectors, 5.5mm-outer is the most common, and I expect most of those to have 2.1mm inner diameter, maybe a few 2.5mm.
But without a pin of known size, it's hard to measure this, even with callipers. Also, there are a lot of barrels that don't have a solid inside but two (spring?) contacts.
So e.g. a socket made for 5.5mm outer, 2.1mm inner diameter will likely also accept 4mm 2.1, and probably 5.5mm 2.5mm. though a 5.5mm outer, 3.4mm inner may not make contact.
However, a socket with a 2.5mm pin won't accept a 2.1mm inner-diameter.
For example, a 5.5mm barrel can come with a 2.1, 2.5, and 3.4mm hole/pin. (...from just the above, more common ones. Less commonly you can apparently also find 1.5, 1.7, 2.8, 3.0, and 3.3mm)
3-Pin and 4-Pin DC Plugs
Doesn't seem to have any singular standard, name, or pinout.
Everyday names seem to include:
- snap and lock (though not all variants lock),
- power mini-DIN, power DIN - misleading as this does not mate with any mini-DIN plugs or sockets, because of the thicker pins than DIN, and often larger shell (the ones I saw were ~10mm instead of mini-DIN's 9.5mm)
Often used to deliver two different voltages, and/or more current than basic DC plugs are comfortable with.
There seem to be a bunch of these, most probably unrelated in origin, probably unified more in "seems solid, had has the two/three/four thick-enough pins I need", some of which seem to be are niche standards.
I should probably try to find more of these, but don't count on it.
JST refers to a company , which make many series of plugs, many of which are PCB connectors useful for data signalling, though many are rated for (on the order of) 2A, and so also useful to transfer some power.
Various JST series
A few of the families:
- PH series: 2.0mm pitch(verify), 2 to 16 pins
- XH series: 2.5mm pitch. Pairs using two slits near on the long ends, near the corner
- Perhaps most recognized as the connector on lithium batteries (2 or more pins depending on how many cells, for balance charging)
- ZH series: 1.5mm pitch, pairs using two slits on the sides (the shortest ends)
- EH series: 2.5mm pitch, pairs with one unshrouded side
- VH series: 3.96mm pitch, clip
- SM series: 2.5mm pitch, matches on a slit in the middle
JST RCY series
Known as the JST connector, BEC connector, P connector
JST ZH series
Seen in cars and such
Cigarette lighter plug
Known as cigar(ette) lighter plug, vehicle receptible, and others. Also called a 12V plug, since this is usually what is provided (some exceptions).
Note that there are technically three variations of this plug, with mildly different sizes. Since many have more than a mm of side-spring they tend to be more or less interchangeable, though it's not always the most comfortable fit.
Mates with an identical plug. Seen in cars, motorcycles, some batteries, some solar panels, and such.
Meant to be wired so that the exposed lead from the power source may safely touch the car chassis.
Mostly seen in RC applications
Pricy, fancy, current-drawing remote controlled vehicles.
Tamiya is regularly seen in RC battery packs. Seems to refer to the plastic's plug/hole shapes (resembles a 2-pin Molex Mini-Fit Jr.) that make this a polarized connection (the square one is positive, the rounded-on-one-side one is ground).
Tamiya seems to be considered a cheapish choice that is good enough for up to a few amps. Or more, depending on the shape and material of the actual connectors(verify).
Also exists in mini variation.
The Deans Ultra connector is a polarized plug made to carry serious current for its size, largely because of the connector shape. Variably listed with ratings between 10A and 30A.
The plug design is a little smaller than things like Tamiya, and not the most shielded choice, but it's rated for more than Tamiya.
There is also a smaller variation of the connector, micro Deams, rated for a dozen amps.
Powerpole - Anderson PowerPoles (also known as sermos) are rated for ~30A. Can be crimped. Larger than other choices, which makes it easier to pull apart than some other higher-amp choices, and lasting somewhat longer.
EC3 is a polarized plastic plug (resembling Tamiya) around bullet/banana-style connectors, and rated to approx 60A. They're relatively cheap(verify), so are handy all-round plugs.
People report them being a little easier to separate than Deans. The plastic may deform when things do heat up, though.
There is a less common larger variant called EC5
Bullet connectors are a solid tube and a solid pin. They may be good for a few dozen or even a hundred amps or so.
Since they are really just two bits of metal, they're probably also the cheapest thing you could call a connector. Of course, without a plug around it (and with some cheap plastic plug designs) you expose metal in ways that easily lets you short things out.
Easily confused with banana plugs. Cheap banana plugs may count on their smallish spring for contact, which means little contact area and so not be good for high currents. Better designed banana connectors may be almost equivalent to bullet plugs.
XT60 is a polarized bullet-based plug rated for ~60A, and uses plastic that deals well with temperature.
Kyosho is comparable to tamiya in rating and also looks similar to it (also resembles EC3 in details).
Also exists in a mini variation.
Higher voltage (mains power)
Refers to IEC 60320 (IEC 320 before the renumbering), the plug/socket system commonly used on devices which can use various socket-to-device wires.
C1 through C24 are defined, and the male and female versions of a type connector have different numbers. Many are polarized. For a few there are variations (e.g. C7/C8), and some are variants of other IEC plugs (e.g. C17/C18 is unearthed variant of C13/C14).
The most common are probably:
- C13/C14, commonly associated with PC power supplies, and other devices that may need its moderate current rating (over e.g. C5/C6), including some professional audio equipment.
- Rated at 10A
- Rated at 16A
- seen where you may need a bit more current than C13/C14 gives, e.g. computer racks may have C19-to-C14 or C19-to-C20 Power Distribution Units
- C5/C6, regularly seen in laptop power supplies and other PC-related power supplies.
- rated for 2.5A
- C7/C8 (a.k.a. 'figure eight', 'shotgun'), unpolarized, ungrounded, is seen on various lower-power devices, from radios to VCRs, some laptop power supplies, game consoles.
- rated at 2.5A
- polarized C7 won't fit into unpolarized C8, which is rarely a problem(verify)
- unpolarised C7 connectors can be inserted into polarized C8 sockets, but this can sometimes be a bad idea
- A little larger than C1/C2
- C1/C2, commonly seen on shavers.
- Rated at 0.2A
- Looks like C7/C8 but without the dents that make it figure-8
Variants with higher temperature rating include:
- C15/C16 has a very similar shape to C13/C14, rated for higher temperatures (120°C)
- e.g. used for electric kettles, and has a dent to prevent mating with C13/C14
- C15A/C16A, similar, (also notched to have a blockier too) rated for 155°C
Power - wall plugs
The types are a less formal(verify) way of indicating the common plugs to use around the world.
Some of the more common plugs are listed below (lettering system as used by some US document on worldwide power)
Type A, Type B, household NEMA variants, JISC C 8303 Class II
(North America, Japan, some other places)
- NEMA 1-15 is a 2-prong non-earthed plug, a.k.a. Type A
- NEMA 5-15 is a 3-prong earthed plug, a.k.a. Type B
- NEMA mentions about two dozen other variations
- some polarized
- most for higher currents, which is why you don't see them in everyday life
- You may have seen NEMA 5-20
- ...where the plug has one blade horizontal...
- ...mostly because the applicable sockets have one T-shaped slot to accept both this and NEMA 5-15 / 1-15, and these sockets are frequent around sturdier installations
Type F / Schuko / CEE 7/4
Type F plugs/sockets, also known as Schuko (short for Schutzkontakt), and formally CEE 7/4, are round sockets/plugs with two earth clips on the side, and two guides for a more robust fit in the socket.
It is used in much of (western) Europe, commonly seen in wall sockets and power strips.
CEE 7/7 plugs
These plugs are designed to be usable in most of Europe and be earthed, by accepting both Type F style earth (western Europe) and Type E style earth (France, Belgium, also Poland, Czech Republic, Slovakia, Denmark).
Seen in wires that must be earthed (so can't be Europlugs) and meant for wide sales (that is, catching both type E and type F countries with the same plug).
Often seen on things like computer power supply cables (with a C17 plug on the other end).
Other, non-earthed European plugs: Type C, CEE 7/16, CEE 7/17, Europlug
The CEE 7/17 plug is a something of an unearthed adaptation of 7/16 to mate with Type E, Type F, and round type C sockets.
There is a (fairly rarely seen) socket that accepts no earthed plugs, by being a type E socket but instead of an earth pin, have a plastic pin and a strip of plastic from where it would be all the way to the edge. This seems to be used on 2-wire extension cords, to make sure you can't plug in an earthed appliance and forget that it isn't actually earthed (...and possibly to be legal to sell at all(verify)).
Type C exists in round and flat variants.
A round Type C socket is typically round, and will accept most any European-style plugs (C, E, F; 7/4, 7/7, others), but is not earthed.
The round type C plug, however, will not plug into Type E or F sockets (blocked by the plastic that guides the earth), so has become rare.
The thin version of Type C, also formalized as CEE 7/16, regularly called a 'Europlug', is an unearthed plug that fits most European-style sockets (Type C, E, F, others).
Power strips sometimes have a few thin-type-C sockets - most people will have a few of these and it saves space, though the sockets accept no other type of plug.
Seen mostly in France, Belgium, Poland, Czech Republic, Slovakia, Denmark
Looks much like Type C, except for the male ground pin that sticks out.
While it has a fixed orientation, there is no polarization standard. (possibly because that would not apply to other european-style plugs it is also compatible with)
Also compatible (mostly things specifically designed for C, E, and F sockets)
- older round type C plugs (unless the socket's male pin is spring-backed and inserts, which is relatively rare(verify))
Type G, BS 1363 (UK)
- polarized in the standard (though many everyday devices won't care)
- Earth prong is longer, so a device is earthed before it gets power
- Sockets may have safety shutters (actuated by the longer earth prong)
- Newer variants have the non-ground pins half shielded so it's very hard to reach live copper
Other apparent design considerations:
- All sockets are the same (there is no unearthed socket design)
- Fuses in the plug - often easier to replace than those in the devices
- Wire from bottom means people won't try to pull it out from the wire, so few break that way (though possibly more break unintentionally)
(Replaced the earlier BS 546 in the 1940s, 1950s)
(australia, some other places)
Exists in a number of variations
- XLR3, seen as:
- XLR5 - in the DMX specs (while many simpler DMX devices use only XLR3, XLR5 is somewhat common on pricier DMX devices)
...and various others, some of which are considered obsolete.
There are also some lesser-seen and specific variants, such as
- PDN to go between amps and speaker
- LNE, that carries just mains power, but was basically never used
The two most recognisable uses are in the event industry, namely
(also note that audio cables and DMX cables, while wires sort-of the same, are not interchangeable for other reasons. It'll work on a test-bench scale, but give issues on large scale)
XLR in pro audio is XLR3, and XLR3 is almost always a mono balanced (differential) line.
Note that there are some audio sockets that take both XLR, and 6.35mm (1/4 inch) TRS, e.g. to save some space on mixers.
You can put stereo on XLR5, but since this isn't very standard, and when plugging things around it's often more convenient to keep everything the same, i.e.e use two XLR3 cables.
XLR and grounding
A particularly fun topic.
Because due to the background, the proper answer to "should XLR be grounded or not?" is "it depends on the case".
The background is that both audio and DMX cables have a shield around the wires, which due to the way shielding works should be connected to a ground somewhere (or it won't work nearly as well).
However, hooking together all shields will at a medium scale easily create ground loops and the related hum, and if you don't know how to solve them properly, the easiest fix is to disconnect that shield on one end.
The reason that that is an issue: is also sometimes the most efficient way to kill people.
This is more of an issue in the audio industry, for several reasons.
- people tend to have "it works this way" background, rather than enough electrical background to know when it is safe
- even that background isn't always enough, in that larger events mean lots of plugging about and no one having full oversight of everything being connected anyway
- shield/ground stuff was ill standardized at first, and then was changed
It also helps that with DMX it's usually hidden on the ceiling, and either works or doesn't - whereas with audio it's easy to find a hum and start poking buttons and yanking things.
See also The_XLR_pin_1_problem
Small mic plugs
Used in some professional audio, as a amp-to-speaker interconnection, i.e. already amplified signal.
It seems to have been introduced to be a non-confusable plug, where before you'd have
- XLR used both as signal cable and as amplified cable, which could damage things.
- TRS that had a similar signal/powered confusion problem (and couldn't deal with as much current, though that doesn't matter for smaller speakers)