Raspberry Pi Board Description

Table of Contents


This page gives a textual description and tour of the layout of the many types of Raspberry Pi.

By reading this page while you hold a Pi in your hands, you should be able to identify the different sockets around the edges of the board, and the GPIO header. Even if you are totally blind, like the author.

The page contains no information about the differences between board versions, such as CPU, clock speed etc., other than to mention the different versions of the Raspberry Pi version 4, which have different amounts of RAM.

For information about differences between Raspberry Pi versions refer to Wikipedia.

Physical Description of a Raspberry Pi

Models 1A and 1A+

Not available at the time of writing.

Note added in December 2020, this model has been discontinued.

Model B

Holding the board with the major components uppermost and the longest sides vertical, like portrait printing mode, and with the very obvious double row of GPIO pins in the bottom left corner; call the top edge north, the long edge to the right east, the short edge closest to you south, and the long edge to your left west.

Going round the board clockwise from north to west:

In the centre of the north edge is the USB socket. This will take 2 USB devices.

To the east of this and still on the northern edge is the ethernet port. You can plug a network cable into this port for a wired connection to a network.

in the centre of the eastern edge of the board is the HDMI video connector. This is for plugging in your HDMI television.

At the eastern side of the southern edge of the board is the micro-USB power socket. This is quite fragile and I’d recommend not repeatedly pulling out the power connector and plugging it back in. To power off the Raspi, once you have cleanly shut-down Linux, simply power off by unplugging the mains adaptor or whatever power source you are using.

In the centre of the underside of the southern edge is the SD card holder. To keep costs low, a very simple plastic card holder has been used. The SD card should be inserted VERY GENTLY with the gold contacts uppermost toward the surface of the board and towards the centre. It is not possible to over-state the need for care in inserting and removing a memory card from this holder. It must be the most fragile part of the whole assembly.

On the western edge, furthest south is the RCA jack for composite video. Many of the now redundant portable analogue televisions in the UK have composite video in so this is a good option if you have one available. Of course, this is video only and does not carry sound.

To the north of this connector is the 3.5mm stereo audio output jack. This is a fairly high impedance output and can produce very loud audio, so careful with those headphones.

That completes the tour of the connectors on the edges of the board.

In the south-west corner of the board is the GPIO header connector. This has two rows of thirteen pins.

The pins are numbered from the south to the north. The row closest to the western edge of the board are numbered evenly from 2 to 26. The row furthest from the western edge are numbered oddly from 1 to 25.

The pin connections vary from revision to revision of the board so pay close attention to the Foundation web pages. I don’t intend to detail the connection orientation of this GPIO header here.

Description of the CSI (Camera Serial Interface) and DSI (Digital Serial Interface) headers will be added when I have the data.

Model 1B+

On July 14 2014 the newer Model B+ was released. Here is a description of this version.

Again holding the board with the obvious GPIO pins uppermost and in the bottom-left corner of the board, call the top edge of the board ‘north’.

From left to right along the north edge there are now two USB connectors, each bearing two USB sockets for a total of four.

At the extreme right edge of the north side is the RJ45 network connector.

On the eastern edge of the board are, from north to south; a 3.5mm jack socket that now carries both the analogue audio and composite video. Then the HDMI monitor connector, then a micro-USB power connector on the upper surface of the board.

In the centre of the southern edge of the board, on the underside, is a micro-SD card holder. This is a spring-loaded push-to-insert and push-to-release socket which is a great improvement on the previous full-sized SD card holder.

On the western edge the only thing of interest is the GPIO bus. This is the double row of pins, a total of forty. This is an increase from the previous Model 1B’s 26 pin header.

The board now has curved corners and four mounting holes which will take M2.5 hardware. There is a hole in each of the south-west and south-east corners, and on the edge of the board just behind the USB and RJ45 connectors on the western and eastern edges respectively.

Model 2B+

In February 2015 the Version 2 Model B+ was released.

This is a quad-core CPU, with twice the RAM and the same very impressive GPU.

Physically, from the point of view of ports and sockets, it is identical to the Model B+.

Raspberry Pi Zero

On the 26th of November 2015, the Raspberry Pi Foundation released an exciting new version of the Raspberry Pi.

This new version is called the Raspberry Pi Zero, and represents a very significant advance in terms of the cost of a RaspberryPi.

At about $5 each, there is a huge saving over the previous versions.

But this is a cut-down board, which is intended to find it’s niche in robotics and Internet-of-things applications.

There are no full-sized USB ports and no Ethernet port. And as supplied there is no GPIO header, although there are holes for soldering in a 40-pin header which is totally pin-compatible with the Model B version 2.

Holding the board in the portrait position, with the three very obvious small ports on the right side, here is a description going round the board…

North edge, no connection. Northern-most on the eastern edge of the board is the power micro-USB connector. Slightly further south is the micro-USB port. I believe this is a USB-otg port. Next on the eastern edge is the micro-HDMI port for connection of a TV/monitor. There is no analogue audio.

On the top surface of the southern edge of the board is a push-pull micro-SD card slot. Unlike the spring-loaded card slot on the B+ and B+2.

In the south-west corner there is a matrix of 40 holes, into which can be soldered a 40-pin IDC header. The pins of this GPIO bus are pin-for-pin compatible with the Model B+ and Model B+ version 2.

That is it. There are no ports for analogue audio or composite video, no ethernet and no full size USB ports.

The CPU is the same SoC as the original Model B, and has 512MB of RAM and a single core.

ZeroW (Wireless)

On 28th February 2017 a new version of the Zero was released. This new version is the same physical layout as the original Zero, with the addition of both WiFi and Bluetooth.

Also, on the northern edge of the board is the CSI camera port.

The ZeroW takes a narrower CSI camera ribbon cable than the full-sized Raspberry Pi.

ZeroWH (Wireless/Header)

This is exactly the same as the ZeroW, but the 40-pin headers are pre-soldered into the supplied board.

Model 3B

On the 29th of February 2016 the Raspberry Pi Foundation released the Model B version 3.

Physically this is identical to the Model B+ version 2, with one notable exception, that it has a friction-fit micro-SD card holder instead of the spring loaded holder of the B+ version 2.

And some LEDs and other things on the board have moved to accomodate other changes like the inclusion of WiFi and Bluetooth.

Refer to the board description of the Model B+ for physical layout.

It fits most, or possibly all cases designed for the Model 2B+

Model 3B+

This model is the same as the 3B, with the addition of a four pin power over Ethernet (PoE) header, situated just behind the left-most USB socket pair, with the board held with the USB sockets uppermost and away from the viewer.

The PoE pins are in a 2x2 pin square.

It is not necessary or advisable to concern yourself with the pin labellings of these four pins. To use PoE you will need either a router provided with PoE capabilities, or an adaptor to plug into the cable between a router and the Pi, with which you can inject a suitable voltage to power the Pi.

You will also need a Raspberry Pi PoE HAT.

Model 4B

Four models of the Raspberry Pi 4 are available, with different amounts of memory:

  • 1GB
  • 2GB
  • 4GB
  • 8GB

The following description is the same for all of the four RAM versions.

Holding the board with the major components uppermost and the longest sides vertical, like portrait printing mode, and with the very obvious double row of GPIO pins in the bottom left corner; call the top edge north, the long edge to the right east, the short edge closest to you south, and the long edge to your left west.

Going round the board clockwise from north to west:

At the extreme left of the north edge is the Ethernet port. Unlike previous versions of the Raspberry Pi, this is full gigabit Ethernet.

Note the Ethernet port has moved from extreme right on this edge to extreme left.

In the centre of the north edge is a pair of vertically stacked USB ports.

In the extreme right corner of the north edge are another pair of stacked USB ports.

From north south, on the eastern edge of the board are the 3.5mm audio/composite video jack, then two micro-HDMI ports. These are smaller than the HDMI ports on all previous versions of the Pi.

Furthest south on the eastern edge is the power socket. This is a USB-C connection. Note that all previous versions of the Pi used a micro-USB power plug. So if you have a power supply which you have previously used with earlier versions, it will not work on a Pi 4.

The current requirements of a Pi 4 are greater than previous versions.

On the underside of the southern edge of the board, in the centre, is the micro-SD card holder. This is friction fit again, rather than spring push/push.

There are no ports on the western edge of the board.

That completes the tour of the connectors on the edges of the board.

In the south-west corner of the board is the GPIO header connector. This has two rows of twenty pins.

The pins are numbered from the south to the north. The row closest to the western edge of the board are numbered evenly from 2 to 40. The row furthest from the western edge are numbered oddly from 1 to 39.

On the top of the board, and just behind the Ethernet port, is the small 2x2 square of pins for the power over Ethernet (PoE) connection.

As before, knowledge of the individual pin functions is not necessary and the best solution for using PoE is to plug in a PoE HAT.

Note that the main chips on the board in Pi version 4 will run hotter than previous versions.

For this reason most suppliers recommend sticking some heat sinks on to the chips and installing a small fan over the SoC. Many cases with integral fans are available.

Description of the CSI (Camera Serial Interface) and DSI (Digital Serial Interface) headers will be added when I have the data.

Model 400

At the time of writing I do not have access to a Raspberry Pi 400, although I do have one on order.

Tim Chase has provided me with an excellent and very comprehensive description of the ports on the back of the keyboard, and the keyboard itself.

Here is a portion of Tim’s email text verbatim, between –snip– tokens:

–snip– If the Pi is on the table in front of you as if you’re about to type and you’re feeling along the back edge, from left to right you have

  • cheap Kensington lock hole
  • wired gigabit ethernet port (though all tests seem to indicate thatthis never actually reaches gigabit speeds)
  • USB 2.0 x1
  • USB 3.0 x2
  • a USB-C power-only port
  • two micro-HDMI (not full-sized) ports which can either drive twosmaller screens or one larger screen (I’d have to go re-researchthose limitations)
  • the micro-SD slot that feels a bit like a 3.5mm audio jack due to its design
  • the 40-pin GPIO header array. Based on what I’ve been able to tell, in this orienation, the top left pin is #1 and the bottomright pin is #40; where if it’s facing you, the the top right pinis #1 and the bottom left pin is #40)

All three non-charging USB ports are traditional USB form-factor, not USB-C or mini or micro or B or whatever

They have several layouts available. The F and J keys do have nubs on them for locating by feel. Here’s the US layout (with the UK layout differences noted below)

Top row #1: Esc, F1 through F10, Num lock, Print-Screen, and Delete

Row #2: standard backtick/tilde, 1 through 0, minus/underscore, plus/equals, backspace

Row #3: standard tab, QWERTYUIOP[/{, ]/}, backslash/pipe

Row #4: standard Caps, ASDFGHJKL, semicolon/colon, single-/double-quote, enter

Row #5: standard shift, ZXCVBNM, comma/less-than, period/greater-than, slash/question-mark, shift

Bottom row #6: ctrl, Function modifier, logo, alt, space, alt, ctrl, and an inverted-T cluster of arrow keys

For several keys you need to use the Fn/Function key in the bottom row:

  • Fn + F1 = F11
  • Fn + F2 = F12
  • Fn + F10 = power button (a bit awkward)
  • Fn + Print Screen = Sys Req
  • Fn + Left = Home
  • Fn + Right = End
  • Fn + Up = Page-up
  • Fn + Down = Page-down

There also appear to be Fn-modifier overlays for a numeric keypad. This is similar to how a lot of smaller laptops array/overlay the numeric keypad. I can’t tell whether that requires holding down the Fn modifier key or if the Num Lock activates them. 7/8/9 and the “/” overlap with the corresponding non-modified keys, 4/5/6 are on U/I/O, 1/2/3 are on J/K/L, 0 is on M, keypad-plus is on the semi-colon/colon key, keypad-minus is on the “P”, and keypad-times is on the zero. As it uses the overlay-style keyboard, there’s no nub on the keypad-5 (which would be confusingly on the letter I)

For what it’s worth, the top right (above the Print Screen key) contains three LED indicators for (left-to-right) num-lock, a red caps-lock, and a green power indicator.

The UK keyboard layout differs slightly:

  • under the escape key is what appears to be backtick, pipe, and alogical “not” (“¬”), instead of the backtick/tilde key
  • the 2 key has the double-quote
  • the 3 key has the “£”
  • the key to the right of semicolon/colon is apostrophe/at-sign
  • to the right of that key (between it and the Enter key) is the”#”/tilde key (slightly narrower than the normal keys)
  • between the left-shift and the Z is the backslash/pipe key
  • where the US keyboard had the backslash/pipe above the one-rowenter-key on the 4th row, the UK layout has a taller enter-key thatspans rows 3 and 4 (and is kinda weirdly shaped, forcing theright-square-bracket key to be slightly smaller, the same size asthe “#”/tilde key below it)

I’m a bit confused regarding the pipe on the UK layout because it appears to be to the left of the number 1 (it appears as a normal broken-pipe character, two smaller vertical lines atop each other with a gap between them) but the key to the left of the Z also has what appears to be a pipe character (an unbroken pipe character, a solid vertical line). Perhaps you have further insight into what that character/key should be.

They sell several other keyboard layouts, but the US and UK versions seem the most widely applicable. –snip–

Additional Notes from me

Thanks to Tim for that. I will be referring to it when my Pi400 arrives, especially the keyboard description, and the Fn key functions.

Note that the ‘traditional’ USB sockets to which Tim refers are USB-A.

About the Kensington Lock hole, I have no experience of these things, but it just appears, from other descriptions, to be a hole in the, admittedly fairly rigid, plastic.

I cannot help thinking this is a poor anti-theft measure, for example, in a school or library.

But of course there may well be Kensington Locks out there which will squawk if the link is broken.

It is a pity the GPIO bus is not provided with a removable cover. As the bus is on the back side of the keyboard, there is some risk of the keyboard being pushed onto something metallic, risking shorting pins together.

I suggest if you do not intend to use the GPIO bus pins, you put a length of tape over it.

Don’t use the common PVC tape referred to commonly as ‘insulating tape’. In my experience the adhesive of this tape bleeds badly and the tape begins to slide about on any non-porous surface to which it is applied.

Duct tape is the best kind of general tape for this kind of application. Duct tape will one day save the world. I believe it already got Apollo 13 back home.

The Raspberry Pi 400 has 4GB of RAM. I have little doubt there will be a Raspberry Pi 800 at some point, with 8GB.

More Notes Added by me Following the Arrival of my Pi 400

On my Pi 400, there is a rubber cover fitted over the GPIO bus. This must be a later addition. The cover is not attached to the keyboard in any way, so I am personally liable to lose it. So I will be fitting some tape over it to prevent this.

The micro-SD slot is the push-push spring loaded type. Not the friction fit used on the Pi models 3 and 4, all variants.

The card goes in with the little raised ridge on the card uppermost and outermost.

The back edge of the card is proud of the back panel of the keyboard by maybe half a millimetre. Be careful when pushing the card to release it. I have found in the past with these spring loaded slots it is very easy for a thumbnail to slip at the wrong moment and for the card to be catapulted into a parallel universe from where you will never recover it. That’s what it feels like when that happens, anyway.