Raspberry Pi A, User Manual, Page: 31 / 314

C H A P T E R 1
M E E T T H E R A S P B E R R Y P I
15
In the centre of all Raspberry Pi boards is a square semiconductor , more commonly known as
an integrated circuit or chip. This is the Broadcom BCM2835 system-on-chip (SoC) module ,
which provides the Pi with its general-purpose processing, graphics rendering and input/
output capabilities. Stacked on top of that chip is another semiconductor, which provides
the Pi with
memory for temporary storage of data while it’s running programs. This type of
memory is known as random access memory (RAM) , as the computer can read from or write to
any part of the memory at any time. RAM is volatile , meaning that anything stored in the
memory is lost when the Pi loses power or is switched off.
Above and below the SoC are the Pi’s video outputs. The silver (bottom) connector is a High
Definition Multimedia Interface (HDMI) port, the same type of connector found on media players
and many satellite and cable set-top boxes. When connected to a modern TV or monitor, the
HDMI port provides high-resolution video and digital audio. The yellow (top) connector is a
com-
posite video port, which is designed for connection to older TVs that don’t have an HDMI socket.
The video quality is lower than is available via HDMI, and there’s no audio; instead, audio is pro-
vided as an analogue signal on the
3.5mm audio jack to the right of the composite video socket.
The pins to the top-left of the Pi compose the general-purpose input-output (GPIO) header ,
which can be used to connect the Pi to other hardware. The most common use for this port is
to connect an
add-on board . A selection of these is described in Chapter 16, “Add-on Boards”.
The GPIO port is extremely powerful, but it’s fragile; when handling the Pi, always take care
to avoid touching these pins, and never connect anything to them while the Pi is switched
on.
The plastic and metal connector below the GPIO port is the Display Serial Interface (DSI) port,
for connecting digitally driven flat-panel display systems. These are rarely used except by
professional embedded developers, as the HDMI port is more flexible. A second plastic and
metal connector, found to the right of the HDMI port, is the
Camera Serial Interface (CSI)
port, which provides a high-speed connection to the Raspberry Pi Camera Module or other
Pi-compatible CSI-connected camera system. For more details on the CSI port, see Chapter
15, “The Raspberry Pi Camera Module”.
To the very bottom-left of the board is the Pi’s power socket . This is a micro-USB socket, the
same type found on most modern smartphones and tablets. Connecting a micro-USB cable
to a suitable power adapter, detailed in Chapter 2, “Getting Started with the Raspberry Pi”,
switches the Raspberry Pi on; unlike a desktop or laptop computer, the Pi doesn’t have a
power switch and will start immediately when power is connected.
On the underside of the Raspberry Pi board on the left-hand side is an SD card slot. A Secure
Digital (SD) memory card provides storage for the operating system, programs, data and other
files, and is
non-volatile ; unlike the volatile RAM, it will retain its information even when power