I/O subsystem

Chapter 3, Processor Elements, introduced two broad categories of I/O architecture: memory-mapped I/O and port-mapped I/O. The pros and cons of each of these approaches were significant in the early days of PCs when the number of physical address lines limited the total processor memory space to a 1 MB range. Modern processor architectures can address a far larger memory range, typically in the tens of gigabytes. A consequence of this address space expansion is the ready availability of address regions for use in I/O interfaces. Because of this, modern 32-bit and 64-bit general-purpose processors employ memory-mapped I/O for most of their interface requirements.

Sophisticated modern processors usually implement a memory controller within the processor chip, communicating directly with DDR memory modules. Most other types of I/O performed by these processors are offloaded to one or more external integrated circuits, typically referred to as a chipset. The term chipset...