CODEWITHSUNDEEP
linux-kernelkernel
Rahul
Rahul

Reputation: 1627

difference between I/O ports and I/O memory

I just want to know the the difference between I/o ports and I/o memory, because I am quite confused. And if someone explain the use of it, that would be great. And by use I mean, when I/O ports are preferred and when I/O memory is preferred.

Upvotes: 8

Views: 5889

Answers (1)

user319198
user319198

Reputation:

There is no conceptual difference between memory regions and I/O regions: both of them are accessed by asserting electrical signals on the address bus and control bus

While some CPU manufacturers implement a single address space in their chips, others decided that peripheral devices are different from memory and, therefore, deserve a separate address space. Some processors (most notably the x86 family) have separate read and write electrical lines for I/O ports and special CPU instructions to access ports.

Linux implements the concept of I/O ports on all computer platforms it runs on, even on platforms where the CPU implements a single address space. The implementation of port access sometimes depends on the specific make and model of the host computer (because different models use different chipsets to map bus transactions into memory address space).

Even if the peripheral bus has a separate address space for I/O ports, not all devices map their registers to I/O ports. While use of I/O ports is common for ISA peripheral boards, most PCI devices map registers into a memory address region. This I/O memory approach is generally preferred, because it doesn't require the use of special-purpose processor instructions; CPU cores access memory much more efficiently, and the compiler has much more freedom in register allocation and addressing-mode selection when accessing memory.

More Details at http://www.makelinux.net/ldd3/chp-9-sect-1

Upvotes: 10

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