Hardware Reference
In-Depth Information
Developed by Acorn Computers back in the late 1980s, the ARM architecture is a relatively
uncommon sight in the desktop world. Where it excels, however, is in mobile devices: the
phone in your pocket almost certainly has at least one ARM-based processing core hidden
away inside. Its combination of a simple reduced instruction set (RISC) architecture and low
power draw make it the perfect choice over desktop chips with high power demands and
complex instruction set (CISC) architectures.
he ARM-based BCM2835 is the secret of how the Raspberry Pi is able to operate on just the
5V 1A power supply provided by the onboard micro-USB port. It's also the reason why you
won't ind any heat-sinks on the device: the chip's low power draw directly translates into
very little waste heat, even during complicated processing tasks.
It does, however, mean that the Raspberry Pi isn't compatible with traditional PC software.
he majority of software for desktops and laptops is built with the x86 instruction set archi-
tecture in mind, as found in processors from the likes of AMD, Intel and VIA. As a result, it
won't run on the ARM-based Raspberry Pi.
he BCM2835 uses a generation of ARM's processor design known as ARM11, which in turn is
designed around a version of the instruction set architecture known as ARMv6. his is worth
remembering: ARMv6 is a lightweight and powerful architecture, but has a rival in the more
advanced ARMv7 architecture used by the ARM Cortex family of processors. Software devel-
oped for ARMv7, like software developed for x86, is sadly not compatible with the Raspberry
Pi's BCM2835—although developers can usually convert the software to make it suitable.
hat's not to say you're going to be restricted in your choices. As you'll discover later in the
topic, there is plenty of software available for the ARMv6 instruction set, and as the Raspberry
Pi's popularity continues to grow, that will only increase. In this topic, you'll also learn how to
create your own software for the Pi even if you have no experience with programming.
Windows vs Linux
Another important diference between the Raspberry Pi and your desktop or laptop, other than
the size and price, is the operating system—the software that allows you to control the computer.
he majority of desktop and laptop computers available today run one of two operating sys-
tems: Microsoft Windows or Apple OS X. Both platforms are
closed source
, created in a secre-
tive environment using proprietary techniques.
hese operating systems are known as closed source for the nature of their
source code
, the
computer-language recipe that tells the system what to do. In closed-source software, this
recipe is kept a closely-guarded secret. Users are able to obtain the inished software, but
never to see how it's made.
