What is this plug, and what fits where? 42 connectors and slots, each drawn the way it looks when you face it, with how to tell it from its look-alikes and the mistakes people make with it. Filter by kind or type a name.
USB-A
USB
The flat rectangular plug on nearly every computer, charger and stick. Fits one way round only.
how to recognise it
Flat rectangle about 12 mm wide with a plastic tongue inside. A blue tongue usually means USB 3 (5 Gbit/s), black or white USB 2, red or yellow a port that charges while the PC is off. Colours are a convention, not a rule.
good to know
A USB 3 device in a black USB 2 port works, at a tenth of the speed. If a backup takes all night, look at the port colour.
Front panel ports hang on a long internal cable. For anything that drops out, test on a rear port first.
USB-B
USB
The square plug on printers, scanners, audio interfaces and some monitors with a built-in hub.
how to recognise it
Nearly square, with two bevelled corners at the top. The USB 3 version is taller with a second block on top and is blue.
good to know
A monitor's USB ports do nothing until this cable goes from the monitor to the PC. It is the most forgotten cable on a desk.
Mini-USB (Mini-B)
USB
Older cameras, GPS units, some external disks and many development boards.
how to recognise it
A small trapezoid about 7 mm wide, clearly thicker than Micro-USB, with sides that narrow towards the bottom.
good to know
Mini and Micro look alike in a drawer and do not fit each other. Mini is the taller one.
Micro-USB (Micro-B)
USB
Phones before about 2017, power banks, headsets, e-readers, Raspberry Pi up to model 3.
how to recognise it
Flat, about 7 mm wide and under 2 mm tall, with two bevelled bottom corners. Fits one way round: the two small hooks are on the flat side.
good to know
The socket wears out long before the cable. A device that charges only when the cable is bent has a worn socket, not a bad battery.
Many cables in the drawer are charge-only and carry no data. If a device charges but does not show up, swap the cable first.
Micro-USB 3.0 (Micro-B SuperSpeed)
USB
External hard disks and disk enclosures from about 2010 to 2020.
how to recognise it
Looks like a Micro-USB plug with a second, rectangular plug attached to its side. About 12 mm wide.
good to know
A normal Micro-USB cable fits into the wider half and works at USB 2 speed, which helps in an emergency.
These plugs are fragile sideways. A disk that disconnects when touched usually needs a new cable, not a new disk.
USB-C
USB
The small oval plug on current notebooks, phones, docks and monitors. Fits both ways round.
how to recognise it
A flat oval, about 8 mm wide, with no up or down. The shape says nothing about what the port can do: look at the symbols next to it.
good to know
Same plug, very different abilities: USB 2 only, 5 to 40 Gbit/s, video or no video, charging with 15 W or 240 W. A battery symbol means the port takes power, a D-shaped symbol means DisplayPort video, a bolt means Thunderbolt.
Cables differ as much as ports. A cable that came with a phone charger often carries USB 2 data only, and no video. For a dock or a monitor, use the cable that came with it.
A dock that works on one notebook and not on another is usually a port that cannot do video, not a broken dock.
Thunderbolt 3, 4 and 5
USB
The fastest kind of USB-C port: docks with several monitors, fast external storage, external graphics.
how to recognise it
A USB-C socket with a small lightning bolt printed next to it. Thunderbolt 1 and 2 used the Mini DisplayPort plug with the same bolt.
good to know
Thunderbolt cables are marked with the bolt and often a number. A plain USB-C cable in between drops the connection to USB speed, or the second monitor stays dark.
On company notebooks, Thunderbolt devices may need approval in the BIOS or in the vendor tool before they work.
HDMI
Video
Monitors, televisions, projectors. Carries picture and sound.
how to recognise it
About 14 mm wide, flat, with the two bottom corners cut in a step. No screws and no latch.
good to know
The plug has not changed since 2003, the abilities have. 4K at 60 Hz needs HDMI 2.0 on both ends and a cable that can do it, otherwise you get 30 Hz, which shows as a mouse pointer that lags.
No sound over HDMI is nearly always the output device selected in the operating system, not the cable.
HDMI to DisplayPort adapters work in one direction only. The cheap ones go from a DisplayPort output to an HDMI screen, not the other way.
Mini and Micro HDMI
Video
Cameras, tablets, single-board computers. Raspberry Pi 4 and 5 use Micro HDMI.
how to recognise it
The HDMI shape, smaller: Mini is about 10 mm wide, Micro about 6 mm and easy to mistake for Micro-USB.
good to know
Micro HDMI sockets break off the board when a stiff cable pulls on them. Use a short flexible adapter.
DisplayPort
Video
Monitors on business PCs, docks and graphics cards.
how to recognise it
About 16 mm wide, rectangular, with exactly one corner cut off. Most plugs have a latch with a release button on top.
good to know
Press the button before you pull. Yanking a latched plug tears the socket out of the monitor.
A monitor that stays black after standby is a known DisplayPort habit. Reseating the cable or switching the monitor off and on brings it back, and a firmware or driver update often cures it.
A DP++ symbol means the port can feed a simple passive HDMI adapter. Without it you need an active adapter.
Mini DisplayPort
Video
Older MacBooks, Microsoft Surface, some graphics cards and docks.
how to recognise it
About 7.5 mm wide, with two cut bottom corners. The same plug with a bolt symbol next to it is Thunderbolt 1 or 2.
good to know
A Thunderbolt 2 display does not work on a plain Mini DisplayPort output, although the plug fits.
DVI
Video
Older monitors and graphics cards.
how to recognise it
Wide white plug with two thumbscrews, a block of square pins and a flat blade at one side. Four extra pins around the blade mean it also carries an analogue signal (DVI-I).
good to know
A DVI to VGA adapter only works on a DVI-I port, the one with the four pins around the blade.
DVI carries no sound. Through an HDMI adapter the picture arrives and the speakers stay silent.
VGA
Video
Old monitors and projectors, and still the console port of many servers.
how to recognise it
Blue, D-shaped, 15 pins in three rows, two thumbscrews.
good to know
Analogue: a blurry or tinted picture is a bad cable or a bent pin. A whole missing colour is one bent pin.
Keep one VGA cable and one small monitor near the server rack. On the day the remote console fails, it is the only way to see anything.
RJ45 (network)
Network
Ethernet: the cable between a computer, a wall socket and a switch. Also used for ISDN and for the console port of switches and routers.
how to recognise it
Clear plastic plug about 11.5 mm wide with eight gold contacts and a spring clip.
good to know
A plug whose clip has broken off slides out by itself and causes outages that come and go. Cut it off and crimp a new one, or throw the cable away.
Link at 100 Mbit/s instead of 1 Gbit/s means one of the four wire pairs is broken: gigabit needs all eight wires, 100 Mbit/s only four.
The console port of a switch looks the same and is a serial port. A normal network cable in it does nothing, and a console cable in a network port neither.
RJ11 and RJ12 (telephone)
Network
Analogue phones, DSL modems, fax machines.
how to recognise it
Like a network plug but narrower, about 9.5 mm, with four or six contacts.
good to know
It fits loosely into a network socket and bends the outer contacts when pushed in. A network port that stopped working after someone plugged a phone in has bent pins.
SFP and SFP+ cage
Network
The slot in a switch, router or network card that takes a transceiver module: fibre, copper, or a direct-attach cable with fixed ends.
how to recognise it
A metal-edged rectangular slot about 14 mm wide, often with a dust plug. SFP (1 Gbit/s) and SFP+ (10 Gbit/s) look identical. The larger QSFP is about 18 mm wide.
good to know
Many vendors accept only their own coded modules. A link that stays down with a third-party module may be a lock, not a fault: the switch log says so.
A 10 Gbit/s module in a 1 Gbit/s slot does not work. The other way round works on most switches, at 1 Gbit/s.
Both ends need the same kind: same speed, same wavelength, same fibre type. Write the module type on the patch panel.
LC fibre connector
Network
The standard fibre plug in data centres and on SFP modules. Usually two together: one fibre sends, one receives.
how to recognise it
Two small square plugs with a clip each, joined by a bracket, with a round white tip in the middle. The older, bigger SC plug is square with push-pull housing.
good to know
Cable colour tells the fibre type: yellow is single-mode, orange, aqua or violet is multi-mode. The two do not mix, and the module must match the fibre.
No link on fibre: swap the two plugs of one end first. Send must meet receive.
Never look into a fibre or a module. Put the dust caps back on: one speck of dust on the tip is enough for errors.
Coaxial F connector
Network
Cable internet modems and satellite receivers.
how to recognise it
A round threaded sleeve with a single thin wire in the centre. Screws on.
good to know
Hand-tight is right. A loose F connector causes exactly the kind of outages that come and go with the weather.
SATA data
Storage
The data cable from the mainboard to a hard disk, SSD or optical drive.
how to recognise it
A thin flat plug about 8 mm wide with an L-shaped opening. Seven contacts.
good to know
Cables without a metal clip work loose. A disk that vanishes now and then, or collects CRC errors in SMART, usually needs a new cable.
Often one of the SATA ports on the mainboard is switched off when an M.2 SSD is installed. The manual has the table.
SATA power
Storage
Power for hard disks and SSDs, coming from the power supply.
how to recognise it
The same L-shape as the data plug but twice as wide, about 15 mm, with 15 contacts. Sits right next to the data plug on the drive.
good to know
Never use a modular power cable from another power supply, even if the plug fits. The pin order on the power supply side differs between brands and models, and the wrong cable puts 12 V on the 5 V line. The drives die instantly.
Cheap Molex to SATA adapters with moulded plugs are a known fire risk. Use crimped ones or a native cable.
SAS (SFF-8482)
Storage
Disks in servers and storage shelves.
how to recognise it
Looks like the SATA data and power plugs in one piece, with the gap between them filled in.
good to know
A SATA disk fits into a SAS bay and works. A SAS disk does not fit a SATA port: the filled gap blocks it, on purpose.
Server bays often accept only disks with the vendor's firmware. A disk shown as "foreign" or "unsupported" is not necessarily broken.
M.2, M key (NVMe)
Storage
Current SSDs. The slot sits flat on the mainboard, and the SSD is held by one screw at the far end.
how to recognise it
One notch near the right end of the contact edge, seen with the label facing you and the contacts pointing down. Five contacts to the right of the notch.
good to know
The notch tells which slot it fits, not how fast it is. An M key SSD is NVMe in nearly every case, and a slot that only does SATA will not see it.
The little screw and the standoff come with the mainboard, not with the SSD. Without the standoff the SSD bends down and loses contact.
Peel the protective film off the heat sink pad before you close the cover.
M.2, B and M key (SATA)
Storage
Older and cheaper M.2 SSDs that use the SATA protocol.
how to recognise it
Two notches: one near the left and one near the right end of the contact edge.
good to know
Fits into an M key slot mechanically. It only works if that slot supports SATA, which many current boards and notebooks no longer do.
In the BIOS it shows up in the SATA list, not in the NVMe list.
M.2, E key (Wi-Fi)
Storage
Wi-Fi and Bluetooth cards in notebooks and on mainboards.
how to recognise it
A short card, usually 22 by 30 mm, with one notch about a third in from one side and two tiny antenna sockets on top.
good to know
An SSD does not fit this slot, and a Wi-Fi card does not fit an SSD slot.
The antenna plugs are tiny and stand only a few insertions. Press them on straight from above, and never pull on the wire.
Some notebook vendors only accept approved cards. An unlisted one stops the machine at start with an error message.
M.2 lengths
Storage
M.2 cards come in several lengths. The number is width and length in millimetres: 2280 is 22 mm wide and 80 mm long.
how to recognise it
Measure from the contact edge to the screw notch. 2280 is the usual desktop and notebook size, 2230 is common in small notebooks, handhelds and Surface devices.
good to know
A shorter card works in a longer slot if the board has a screw position for it, or with a small extender. A longer card never fits.
Before you buy an SSD for a notebook, open it or read the service manual: 2230-only machines are common.
mSATA and Mini PCIe
Storage
Small cards in notebooks and mini PCs from about 2009 to 2015: SSDs, Wi-Fi and mobile data cards.
how to recognise it
A card about 30 mm wide with one notch off-centre in the contact edge and two screw holes at the far end. Half-size cards are 27 mm long, full-size 51 mm.
good to know
mSATA and Mini PCIe use the same connector with different signals. An mSATA SSD in a Mini PCIe Wi-Fi slot fits and does not work. The manual says which slot is which.
ATX 24-pin
Power inside the PC
Main power from the power supply to the mainboard.
how to recognise it
The largest plug in the PC: two rows of twelve, with a clip in the middle of one long side. Often built as 20+4, with four pins that can be split off.
good to know
It needs real force and the clip must click. A plug that sits 2 mm high causes the strangest faults: no start, or restarts under load.
Press the clip before you pull, and pull on the plug, not on the wires.
CPU power, 8-pin EPS (4+4)
Power inside the PC
Power for the processor, plugged in near the top left of the mainboard.
how to recognise it
Two rows of four. Usually built as two halves of four pins that slide together. The cable is labelled CPU.
good to know
A PC where fans spin and nothing else happens: this plug was forgotten. It is the most common mistake in a new build.
Looks like the graphics card plug and is wired the other way round. They are keyed so that they should not fit: never force a power plug.
Graphics card power, PCIe 8-pin (6+2)
Power inside the PC
Extra power for a graphics card.
how to recognise it
Two rows of four, built as a block of six with a separate block of two that hangs next to it. The cable is labelled PCIe or VGA.
good to know
Two plugs on one cable (a pigtail) are fine for a mid-range card. A power-hungry card should get a separate cable for each socket.
Cables of a modular power supply belong to that model. Kept in the box of the power supply, they do not end up in another PC.
12VHPWR and 12V-2x6
Power inside the PC
Power for current high-end graphics cards, up to 600 W through one plug.
how to recognise it
Two rows of six small pins, with four tiny sense pins in a row underneath.
good to know
It must be pushed in completely and click, and the cable must run straight for the first 3 to 4 cm. Plugs that sat at an angle have melted.
Check it again after moving the PC.
Molex, 4-pin peripheral
Power inside the PC
Old drives, case fans, pumps, and adapters to almost everything.
how to recognise it
A white or black plug about 21 mm wide with two bevelled corners and four round pins.
good to know
The pins sit loosely in the housing. If it will not go in, one pin is crooked: straighten it with a small screwdriver instead of pushing harder.
Carries 12 V and 5 V. A fan running on a Molex adapter always runs at full speed.
Fan header, 3-pin and 4-pin
Power inside the PC
Case and CPU fans on the mainboard.
how to recognise it
A row of three or four pins with a plastic tab behind them. The plug has a groove that slides over the tab.
good to know
A 3-pin fan fits a 4-pin header and the other way round, the tab makes sure of the position. With the fourth pin the board controls the speed precisely (PWM), with three it can only vary the voltage.
The header labelled CPU_FAN must have a fan, or many boards refuse to start with a "CPU fan error". With water cooling, put the pump or a radiator fan there.
IEC C13 and C14 (the PC power cord)
Mains and external power
PCs, monitors, printers, most servers and switches.
how to recognise it
A plug with three flat pins in a row-of-one over row-of-two pattern and two bevelled corners.
good to know
Rated for 10 A. In a rack, cords with a lock (a coloured slider) stop a plug from being pulled out by accident.
The version with a notch (C15) is for hot devices such as kettles and some switches. A C15 cord fits a C14 inlet, a C13 cord does not fit a C16 inlet.
IEC C5 and C6 (cloverleaf)
Mains and external power
Notebook power supplies, projectors, some monitors.
how to recognise it
Three round pins in a housing shaped like a three-leaf clover.
good to know
Earthed, unlike the figure-8 cord. A tingling feeling on a metal notebook case usually means someone replaced it with an unearthed adapter.
IEC C7 and C8 (figure-8)
Mains and external power
Small power supplies, radios, consoles, printers, Apple chargers.
how to recognise it
Two round pins in a flat housing with a waist, like the number 8 lying down. No earth.
good to know
Rated for 2.5 A only. Fine for a notebook charger, not for anything with a heater.
IEC C19 and C20
Mains and external power
Large servers, blade chassis, big UPS units and the power strips (PDUs) in a rack.
how to recognise it
Bigger than the PC plug, rectangular, with three flat pins lying horizontally.
good to know
Rated for 16 A. If a new server arrives with these cords and the rack only has C13 sockets, the power strip is the wrong one: do not use an adapter cord, it defeats the rating.
Count the amps per power strip before you add a server. A tripped rack breaker takes everything on that strip down at once.
Barrel plug (DC)
Mains and external power
The round plug of external power supplies: routers, switches, monitors, older notebooks.
how to recognise it
A metal sleeve with a hole in the middle, 3.5 to 7.4 mm across. Dozens of sizes exist.
good to know
The plug fitting says nothing. Check three things on the label of the device and the power supply: the voltage must match exactly, the amps of the supply must be the same or higher, and the polarity symbol must be the same.
A router with the wrong power supply may run for weeks and then act strangely: restarts, weak Wi-Fi. Label power supplies with the device they belong to.
Memory modules: DIMM and SO-DIMM
Memory and slots
Main memory. DIMM in desktops and servers, the shorter SO-DIMM in notebooks and mini PCs.
how to recognise it
DIMM is 133 mm long, SO-DIMM 68 mm. The notch in the contact edge sits in a different place for each generation, so DDR3, DDR4 and DDR5 cannot be mixed up by force, only by purchase.
good to know
Check the generation before buying: it is printed on the old module's label (PC4 is DDR4, PC5 is DDR5).
A DIMM needs a firm push at both ends until both clips snap. Half-seated memory is the classic cause of a PC that will not start after being moved.
Servers take registered modules with error correction (RDIMM), desktops take unbuffered ones (UDIMM). They are not interchangeable, although the notch may let them in.
In many thin notebooks the memory is soldered on and cannot be changed.
Slots of four lengths, named after the number of lanes: x1 is about 25 mm long, x16 about 89 mm. A small ridge divides the short power section from the data section.
good to know
A shorter card works in a longer slot. That is by design.
A long slot is not always fully wired: an x16-sized slot may only carry four lanes. The board prints it next to the slot, or the manual says so.
Before pulling a graphics card, release the latch at the end of the slot. It hides under the card and breaks easily.
A new card that is not detected: reseat it, then check whether the slot shares lanes with an M.2 slot and is switched off.
3.5 mm audio jack
Audio and legacy
Headphones, headsets, speakers.
how to recognise it
A 3.5 mm pin. Two rings on the plug mean stereo sound, three rings mean stereo plus microphone (a headset plug).
good to know
A notebook with one combined socket needs a three-ring plug for the microphone. A PC with separate green and pink sockets needs a Y adapter for a headset.
Humming speakers on a PC: try the rear socket instead of the front one, the front cable picks up noise.
Serial port, DB9 (RS-232)
Audio and legacy
Console access to switches, firewalls, UPS units, and machines on the factory floor.
how to recognise it
D-shaped, nine pins in two rows, two screws. Smaller than VGA and with fewer, thicker pins.
good to know
Notebooks have none: keep a USB to serial adapter with a known good chip in the bag, and test it before you stand in front of a dead switch.
The usual settings to start with are 9600 baud, 8 data bits, no parity, 1 stop bit. Garbage on the screen means the speed is wrong.
Newer devices have the console on an RJ45 socket or on USB instead. The pinout of RJ45 console cables differs between vendors.
PS/2
Audio and legacy
Keyboards and mice before USB. Still on some mainboards and on KVM switches.
how to recognise it
Round, 6 pins, with a plastic block that only lets it in one way. Purple for the keyboard, green for the mouse.
good to know
Not hot-pluggable: plug it in before the PC starts.
Worth keeping one PS/2 keyboard: it works in a BIOS that does not react to USB keyboards.
Nothing matches. Try a shorter word, or the shape: round, flat, square.