The Model B Rev 2.0 Raspberry Pi has 512 MB of SDRAM, while the older revisions and remaining models have 256 MB. Contrast this to the AVR class ATmega168p, which has 1 KB of static RAM. SDRAM is synchronous dynamic random access memory, which synchronizes with the system bus for improved performance. It uses a form of pipelining to gain this advantage.
There isn’t much about the memory hardware that concerns the average Pi developer. However, in this chapter, you’ll examine some useful Raspbian Linux kernel interfaces that inform us how that memory is utilized. You’ll also examine how to access the memory-mapped ARM peripherals ...