The Raspberry Pi is powered by a Broadcom BCM2835 System on a Chip. But there are millions of other devices, all powered by similar means.
Here we'll explain what an SoC is, what it does, and why they exist.
In very broad terms, a System on Chip is a microchip that has all the components required to power a computer. In the case of the Raspberry Pi, the Broadcom chip contains a 700MHz ARM processor and a Videocore 4 GPU.
Q. Are all SoCs so low on processing power?
A. Not at all. The RPi has different priorities than other devices that use SoCs. In fact, newer SoCs sport multi-core processors and GPUs.
Q. But so does my motherboard. How are SoCs any different?
A. First, there's the fact that on a motherboard the different components are housed in separate chips. So there's a CPU, there's a graphics processor, there's memory, and so on. On the other hand, a System on a Chip has all these components on a single chip, and is hardly any bigger than the traditional CPU.
Q. Ah! Is this the reason why the RPi is so puny?
A. Absolutely! A computer needs various components, and while a desktop has room to easily fit them all, it would be virtually impossible on a device like the RPi. Thanks to System on a Chip, we have powerful computers in a much smaller form factor, like a smartphone, with spare room for the batteries.
Q. And that's another advantage, right? These devices don't need a lot of power.
A. That's right, and this is thanks to the very tight integration of the components, which doesn't require much wiring; and this in turn makes these devices a lot more efficient. Take the RPi for example, which only needs 5V to run via the Micro USB type B. In fact, I powered mine using my smartphone's charger!
Q. So, besides the RPi and smartphones, are there any other types of devices that use SoC?
A. If a device fits in your hand and runs on batteries, chances are it's powered by an SoC. So, in addition to smartphones, tablets too are powered by SoCs. In fact, most of the popular Android tablets are powered by Nvidia Tegra 3 and Qualcom Snapdragon SoCs. Even the Microsoft Surface Tab will be powered by the Tegra 3 SoC.
Q. That's awesome! Talking of the RPi, when you mentioned its Broadcom chip, you said it's got a CPU and a GPU. So where's the memory?
A. Well, the revision 2 RPi uses 512MB of SDRAM, and it's stacked right on top of the Broadcom chip via a technology called package-on-package, or PoP.
Q. PoP? Sounds like a quick and cheap fix to a leaking roof.
A. You might be closer than you realise, at least in the quick and cheap sense. Sometimes, it's just not feasible to build an SoC for a particular type of device. On smaller devices, like the RPi and other popular open source hardware devices like the BeagleBoard, manufacturers save space (and money) by piling multiple chips, or "packages" as they'd like to call them, on top of each other.
Q. I'm guessing they don't just glue them on top of each other?
A. The SoC chips use a surface mount technology known as ball grid array. The SoC chips are lined with tiny interconnection pins on both the top and bottom. The manufacturers then solder the lower ones to connect the SoC to the board, and use the ones on the top to connect memory packages. This gives them more flexibility, as they can use the memory from different vendors. For example, some RPi boards have memory from Hynix and others from Samsung.
